Cardiovascular system — AQA A-Level Physical Education

The cardiovascular system is a central topic in AQA A-Level Physical Education, covering the structure and function of the heart, blood vessels and blood. It explains how oxygen and nutrients are transported to working muscles and how waste products such as carbon dioxide are removed. Understanding the cardiac cycle, conduction system and vascular shunting is essential for analysing how the body meets the demands of physical activity.

This topic links closely with the respiratory and energy systems, and it underpins later work on training adaptations, VO2 max and sports performance. Students must be able to describe acute responses to exercise, such as increased heart rate and redistribution of blood flow, and chronic adaptations following training, such as bradycardia and increased stroke volume. Exam questions often require application to specific sports and evaluation of how these changes affect performance.

• →The heart has four chambers: right atrium and ventricle receive deoxygenated blood from the body and pump it to the lungs; left atrium and ventricle receive oxygenated blood from the lungs and pump it to the body via the aorta.
• →The conduction system: the sinoatrial node (SAN) initiates impulses, the atrioventricular node (AVN) delays the impulse to allow ventricular filling, and the bundle of His and Purkinje fibres spread the impulse through the ventricles.
• →The cardiac cycle consists of atrial systole, ventricular systole and diastole, with pressure changes causing valves to open and close, producing heart sounds.
• →Vascular shunting redistributes blood during exercise: vasodilation of arterioles in working muscles and vasoconstriction in non-essential areas, controlled by the vasomotor centre.
• →Venous return is aided by the skeletal muscle pump, respiratory pump, pocket valves and smooth muscle in veins, ensuring blood returns to the right atrium.

• Regular physical activity induces cardiac hypertrophy, increasing stroke volume and maximal cardiac output.
• Training lowers resting heart rate (bradycardia) and improves the efficiency of oxygen transport to working muscles.
• Physical activity reduces the risk of hypokinetic diseases, such as coronary heart disease and stroke.
• Health benefits include lowered resting blood pressure, improved capillarisation and increased high-density lipoproteins.
• Heart disease: coronary arteries narrowed by fatty plaque, reducing oxygen supply to cardiac muscle and causing angina or myocardial infarction.
• High blood pressure: persistently raised pressure in arteries increases cardiac workload and damages artery walls.
• Cholesterol: low-density lipoprotein cholesterol contributes to plaque formation; high-density lipoprotein cholesterol helps remove cholesterol from arteries.
• Stroke: interrupted blood supply to the brain, often from a clot or burst vessel, causing brain cell damage.
• Interactions: raised cholesterol can worsen plaque build-up, which can raise blood pressure and increase heart disease and stroke risk.
• Cardiac output is the product of heart rate and stroke volume: Q = HR × SV.
• At rest, trained individuals typically have a lower resting heart rate and a larger stroke volume than untrained individuals, with similar resting cardiac output.
• During maximal exercise, trained individuals achieve a higher maximal cardiac output, mainly through a greater stroke volume.
• During sub-maximal exercise, trained individuals produce a given cardiac output at a lower heart rate than untrained individuals.
• These adaptations improve oxygen delivery to working muscles and support endurance performance.
• Neural regulation: the cardiovascular control centre in the medulla alters sympathetic and parasympathetic (vagal) outflow to the sinoatrial node.
• Sympathetic stimulation increases heart rate, stroke volume and cardiac output; parasympathetic stimulation reduces heart rate at rest.
• Hormonal regulation: adrenaline and noradrenaline from the adrenal medulla increase heart rate, stroke volume and contractile force.
• Chemical regulation: chemoreceptors detect increased carbon dioxide, decreased pH and reduced oxygen, and baroreceptors detect changes in blood pressure.
• Proprioceptors detect movement and inform the control centre, so heart rate rises before and during activity.
• The combined effect is a rise in cardiac output and redistribution of blood to active muscles.
• Anticipatory rise is an increase in heart rate before exercise starts, caused by anticipation of the activity.
• The cerebral cortex and limbic system stimulate the medullary cardiovascular control centre.
• Sympathetic outflow to the sinoatrial node increases and parasympathetic (vagal) tone decreases.
• Adrenaline and noradrenaline from the adrenal medulla reinforce the rise in heart rate.
• Proprioceptor input as movement begins adds to the response.
• The effect is a higher cardiac output at the start of exercise, which reduces the initial oxygen deficit.
• Vascular shunting is the redistribution of blood flow to areas of greatest demand during exercise.
• Vasodilation widens arterioles supplying working muscles, increasing local blood flow and oxygen delivery.
• Vasoconstriction narrows arterioles supplying non-essential organs such as the gut and kidneys, diverting blood away.
• The vasomotor centre in the medulla oblongata controls sympathetic outflow to arterioles.
• Pre-capillary sphincters open or close to direct blood through specific capillary beds.
• Skin blood flow increases to aid heat loss, while the proportion of cardiac output to skeletal muscle rises.
• The sinoatrial node (SA node) initiates the impulse and acts as the pacemaker.
• The impulse spreads through the atria, causing atrial systole.
• The atrioventricular node (AV node) delays the impulse to allow atrial emptying before ventricular contraction.
• The impulse travels down the bundle of His and bundle branches to the Purkinje fibres.
• Purkinje fibres stimulate ventricular contraction from the apex upwards.
• The sequence ensures atria contract before ventricles, and autonomic nerves modify heart rate.
• Sympathetic stimulation increases heart rate by raising the firing rate of the sinoatrial node.
• Sympathetic stimulation increases stroke volume and therefore cardiac output during exercise.
• Parasympathetic stimulation decreases heart rate by slowing the firing rate of the sinoatrial node.
• Parasympathetic activity dominates at rest and during recovery from exercise.
• The two divisions form an antagonistic pair whose balance sets the current heart rate.
• Sympathetic activity is mediated by noradrenaline and parasympathetic activity by acetylcholine at the sinoatrial node.
• Carbon dioxide is produced by aerobic respiration in exercising muscle.
• Rising carbon dioxide in the blood is detected by chemoreceptors.
• Increased carbon dioxide and the associated fall in pH increase sympathetic stimulation of the sinoatrial node.
• The result is an increased heart rate and cardiac output during exercise.
• Carbon dioxide contributes to local vasodilation in active muscle, increasing blood flow to working tissue.
• Vascular shunting directs blood towards active muscle and away from less active areas.
• Chemoreceptors detect chemical changes in the blood, including rising carbon dioxide and falling pH, and falling oxygen levels.
• Proprioceptors detect movement and changes in muscle and joint position, informing the brain that exercise has started.
• Baroreceptors detect stretch of blood vessel walls and therefore changes in blood pressure.
• Receptor information is sent to the medulla oblongata, which regulates heart rate and blood vessel diameter via the autonomic nervous system.
• Sympathetic stimulation increases heart rate and vasoconstriction, while parasympathetic stimulation slows heart rate at rest.
• The overall purpose is to match blood flow and oxygen delivery to the increased metabolic demand of physical activity.
• Chemoreceptors detect changes in blood chemistry, particularly increased carbon dioxide, decreased pH and decreased oxygen.
• Proprioceptors detect movement and changes in muscle and joint position during physical activity.
• Baroreceptors detect stretch of blood vessel walls, providing information about blood pressure.
• All three receptor types send impulses to the medulla oblongata, which coordinates cardiovascular regulation.
• The medulla oblongata responds by altering sympathetic and parasympathetic outflow to the sinoatrial node and blood vessels.
• These responses increase heart rate, stroke volume and redistribute blood flow to meet the demands of exercise.
• Oxygen is transported in blood in two forms: a small amount dissolved in plasma and the majority bound to haemoglobin within red blood cells.
• Oxygen has low solubility in plasma, so dissolved transport alone is insufficient to meet the oxygen demand of working muscles.
• At the alveoli, oxygen diffuses into the blood down a partial pressure gradient and combines with haemoglobin to form oxyhaemoglobin.
• At respiring tissues, the lower partial pressure of oxygen causes oxyhaemoglobin to dissociate, releasing oxygen that diffuses into the cells.
• During exercise, increased cardiac output and redistribution of blood flow increase the rate at which oxygen is delivered to active muscles.
• The arteriovenous oxygen difference widens during exercise because more oxygen is extracted by the working tissues.
• Haemoglobin is an iron-containing protein found in red blood cells that binds oxygen reversibly.
• Each haemoglobin molecule can bind up to four oxygen molecules, forming oxyhaemoglobin.
• Oxygen binds to haemoglobin at the lungs where the partial pressure of oxygen is high.
• Oxyhaemoglobin dissociates at respiring tissues where the partial pressure of oxygen is lower, releasing oxygen.
• Increased carbon dioxide and acidity in active muscle reduce haemoglobin's affinity for oxygen, increasing oxygen unloading during exercise.
• The reversible binding of oxygen allows haemoglobin to transport oxygen from the lungs to the tissues.
• Myoglobin is an oxygen-binding pigment located in skeletal muscle (sarcoplasm), not in red blood cells.
• It contains one haem group and one globular protein chain, so it binds one molecule of O₂ per molecule.
• It has a higher affinity for oxygen than haemoglobin at any given partial pressure of oxygen.
• It acts as a short-term oxygen store within muscle and releases oxygen when partial pressure of oxygen falls during contraction.
• The oxygen it releases supports aerobic respiration in the mitochondria of working muscle fibres.
• It contributes to the red colour of slow-twitch (type I) muscle fibres.
• The curve plots percentage saturation of haemoglobin with oxygen on the y-axis against partial pressure of oxygen (pO₂) on the x-axis.
• The curve is sigmoid (S-shaped) because of cooperative binding: the first oxygen molecule bound alters haemoglobin's shape and increases its affinity for further oxygen molecules.
• At high pO₂ in the lungs, haemoglobin has a high affinity for oxygen and becomes almost fully saturated, forming oxyhaemoglobin.
• At low pO₂ in respiring tissues, haemoglobin's affinity for oxygen decreases and oxygen dissociates to be used in aerobic respiration.
• The Bohr shift moves the curve to the right when carbon dioxide concentration increases, pH decreases or temperature rises during exercise, so more oxygen is released at the same pO₂.
• Myoglobin's dissociation curve lies to the left of haemoglobin's, reflecting its higher affinity for oxygen.
• Carbon dioxide concentration increases during exercise because respiring muscles produce more carbon dioxide.
• Increased carbon dioxide lowers blood pH, making the blood more acidic.
• Lower pH reduces haemoglobin's affinity for oxygen.
• The oxyhaemoglobin dissociation curve shifts to the right.
• At a given partial pressure of oxygen, haemoglobin saturation is lower, so more oxygen dissociates.
• More oxygen is therefore delivered to the active muscles.
• Venous return is the volume of blood returning to the heart per minute.
• The skeletal muscle pump: contracting muscles compress veins, and valves ensure one-way flow.
• The respiratory pump: pressure changes in the thorax and abdomen during breathing assist flow towards the heart.
• Valves in veins prevent the backflow of blood.
• Smooth muscle and elastic recoil in vein walls maintain venous tone and help propel blood.
• Increased venous return raises stroke volume and cardiac output via the Frank-Starling mechanism.
• Cardiac output is the product of heart rate and stroke volume, so changes in either variable alter the volume of blood pumped per minute.
• The cardiac control centre in the medulla oblongata regulates heart rate through the sympathetic and parasympathetic nervous systems.
• Chemoreceptors detect changes in blood carbon dioxide and pH, while baroreceptors detect changes in blood pressure, and both feed information back to the control centre.
• The vascular shunt redirects blood flow: vasoconstriction reduces flow to non-essential areas such as the digestive system, while vasodilation increases flow to working muscles.
• Venous return is assisted by the skeletal muscle pump, the respiratory pump and one-way valves in the veins, which prevent backflow.
• Systolic pressure is the pressure in the arteries when the ventricles contract and eject blood.
• Diastolic pressure is the pressure in the arteries when the ventricles relax and refill.
• Blood pressure is recorded as systolic over diastolic, for example 120/80 mmHg.
• During exercise, systolic pressure increases because cardiac output and the force of ventricular contraction rise.
• Diastolic pressure changes little or may decrease during exercise because vasodilation in working muscles lowers peripheral resistance.
• Starling's law links the degree of stretch of ventricular muscle to the force of contraction.
• Greater venous return increases end-diastolic volume and stretches the ventricular walls.
• Increased stretch raises the force of ventricular contraction, increasing stroke volume.
• Cardiac output equals heart rate multiplied by stroke volume, so a rise in stroke volume raises cardiac output.
• The skeletal muscle pump and respiratory pump increase venous return during exercise.
• The relationship has a limit: excessive filling can reduce the effectiveness of contraction.
• Cardiovascular drift occurs during prolonged steady-state exercise, particularly in hot conditions.
• Plasma volume decreases through sweating and fluid shifts, reducing venous return.
• Stroke volume falls as venous return and ventricular filling decrease.
• Heart rate rises progressively to maintain cardiac output at the required level.
• Cardiac output is maintained because heart rate increases as stroke volume decreases.
• The drift reflects thermoregulatory and fluid-balance challenges during prolonged exercise.
• Defines A-VO₂ diff as the difference in oxygen content between arterial blood and venous blood.
• States that it is calculated by subtracting venous oxygen content from arterial oxygen content.
• Explains that a larger A-VO₂ diff indicates greater oxygen extraction by the tissues, especially working muscles.
• Recognises that the difference widens during exercise and is smaller at rest.
• Uses correct units, such as cm³ of oxygen per 100 cm³ of blood, when quoting values.
• Identifies that individuals vary in heart rate, stroke volume, cardiac output, blood pressure and A-VO₂ diff responses to the same session.
• Explains that training status affects the size and speed of the response, with trained performers often showing a lower resting heart rate and larger stroke volume.
• Names additional factors such as age, sex, body composition, hydration, temperature and emotional state.
• Recognises that the same absolute workload can produce different responses in different people.
• Uses correct units, such as beats per minute for heart rate and dm³ per minute for cardiac output.
• Trained individuals typically have a lower resting heart rate than untrained individuals because stroke volume is larger.
• Trained individuals typically have a greater stroke volume at rest and during exercise because the left ventricle fills and contracts more effectively.
• Cardiac output at rest may be similar in trained and untrained individuals because a lower heart rate can offset a larger stroke volume.
• During submaximal exercise, a trained individual reaches a given oxygen uptake at a lower heart rate than an untrained individual.
• During maximal exercise, a trained individual can achieve a higher cardiac output and a higher maximum oxygen uptake.
• Differences are explained by cardiovascular adaptations such as cardiac hypertrophy, increased stroke volume and improved venous return.
• Cardiovascular adaptations include cardiac hypertrophy, increased stroke volume, increased capillary density and improved venous return.
• Respiratory adaptations include strengthened respiratory muscles and increased lung volumes and capacities, supporting greater oxygen uptake.
• Muscular adaptations include increased mitochondria, increased myoglobin and increased aerobic enzyme activity, improving oxygen extraction and use.
• The combined adaptations lower resting heart rate, improve recovery and increase maximum oxygen uptake.
• The training effect is the improved capacity to perform aerobic exercise produced by these system adaptations.
• Adaptations are specific to the type and intensity of training undertaken.

• 💡Define health and fitness precisely before explaining their relationship to the cardiovascular system.
• 💡Use specific examples of cardiovascular adaptations (e.g. increased stroke volume, bradycardia) to support your answer.
• 💡In multiple-choice questions, reject options that claim training increases maximum heart rate.
• 💡Read the question carefully to identify whether it asks about a cause, a mechanism or a health consequence.
• 💡Link each condition to its effect on blood flow or oxygen delivery, not just its name.
• 💡Eliminate options that confuse the heart and the brain, or that treat all cholesterol as harmful.
• 💡Use the equation Q = HR × SV to check whether an option is numerically possible.
• 💡Compare trained and untrained responses at rest, during sub-maximal exercise and during maximal exercise separately.
• 💡Look for options that confuse heart rate with stroke volume or that ignore the effect of training.
• 💡Name the receptor type and the specific change it detects, rather than writing only that receptors detect exercise.
• 💡Link each control route to a measurable effect such as heart rate, stroke volume or cardiac output.
• 💡Use correct terminology: sinoatrial node, medulla, sympathetic, parasympathetic, adrenal medulla.
• 💡Check that each option in a multiple-choice question matches the control route named in the stem.
• 💡State clearly that the rise occurs before exercise, not during it.
• 💡Name the control centre and the autonomic branches involved.
• 💡Link the response to its purpose: increased oxygen delivery and reduced oxygen deficit at the start of activity.
• 💡Read multiple-choice options carefully for words such as before, during and after.
• 💡In an MCQ, eliminate options that reverse the sites of vasodilation and vasoconstriction.
• 💡Link each vessel change to its purpose: more oxygen to muscles, heat loss at the skin, blood diverted from the gut.
• 💡Use precise terms such as arterioles, lumen and vasomotor centre rather than vague words like tubes or brain.
• 💡In an MCQ, check the order of structures: SA node, atria, AV node, bundle of His, bundle branches, Purkinje fibres.
• 💡Match each structure to its function rather than just its name.
• 💡Remember the AV nodal delay is essential for efficient ventricular filling.
• 💡Link each division to a specific effect at the sinoatrial node rather than writing only that it speeds up or slows down the heart.
• 💡Use the antagonistic pair idea to explain changes across exercise and recovery in one continuous account.
• 💡Check that any heart-rate value you quote is consistent with the direction of the division you have named.
• 💡Name the receptor type and the structure it acts on, for example chemoreceptors leading to increased sympathetic stimulation of the sinoatrial node.
• 💡Link the carbon dioxide stimulus to a measurable outcome such as increased heart rate, stroke volume or cardiac output.
• 💡Use the term vasodilation accurately and state where it occurs, for example in active muscle.
• 💡Keep the sequence of cause and effect explicit so the marker can follow the pathway from production to response.
• 💡Link each receptor to the specific stimulus it detects, then state the response that follows, such as increased heart rate.
• 💡Use the correct pathway: receptor detects change, sends impulse to medulla oblongata, autonomic nervous system alters heart rate or vessel diameter.
• 💡Apply each receptor to a concrete exercise context, for example proprioceptors firing at the start of a sprint and chemoreceptors responding as carbon dioxide rises.
• 💡Create a three-column summary linking each receptor to its stimulus, location and resulting cardiovascular response.
• 💡Practise explaining the full pathway from receptor detection through the medulla oblongata to the effector response in the heart or blood vessels.
• 💡Use exercise examples such as sprinting or cycling to show how each receptor contributes to regulating responses during physical activity.
• 💡Link each transport step to a partial pressure gradient so the direction of oxygen movement is explicit.
• 💡Use the terms oxyhaemoglobin and dissociation accurately when describing loading at the lungs and unloading at the tissues.
• 💡When a question mentions exercise, connect oxygen transport to increased cardiac output and greater oxygen extraction by active muscle.
• 💡Use the terms loading and dissociation to describe oxygen binding at the lungs and release at the tissues.
• 💡Refer to the partial pressure of oxygen when explaining why haemoglobin binds or releases oxygen.
• 💡Link reduced haemoglobin affinity in active muscle to increased carbon dioxide and acidity when explaining oxygen unloading during exercise.
• 💡Read the stem carefully to check whether the question asks about location, structure or function before choosing an option.
• 💡Compare myoglobin with haemoglobin explicitly: one haem group versus four, muscle versus red blood cell, higher versus lower affinity.
• 💡Link myoglobin to the dissociation curve by noting that its curve sits to the left of the haemoglobin curve at the same partial pressure of oxygen.
• 💡Eliminate options that place myoglobin in blood plasma or describe it as an enzyme rather than an oxygen-binding pigment.
• 💡Check which variable is on each axis before interpreting the curve in an MCQ option.
• 💡Use the terms 'loads' at the lungs and 'unloads' or 'dissociates' at the tissues to describe the two ends of the curve.
• 💡Link the Bohr shift to exercise by naming the specific changes: increased carbon dioxide, increased temperature and decreased pH.
• 💡Compare the myoglobin curve with the haemoglobin curve by stating that myoglobin sits to the left because of its higher oxygen affinity.
• 💡Link the shift explicitly to exercise so the answer explains why more oxygen reaches active muscle.
• 💡Use the phrase 'reduced affinity of haemoglobin for oxygen' rather than saying haemoglobin 'holds less oxygen'.
• 💡When a graph is given, quote the partial pressure of oxygen and compare the two saturation values at that point.
• 💡State the causal chain in order: more carbon dioxide, lower pH, reduced affinity, rightward shift, greater dissociation.
• 💡Name each mechanism and then state exactly how it moves blood towards the heart.
• 💡Use the term 'one-way flow' when describing the role of valves.
• 💡Link venous return to stroke volume and cardiac output to show why it matters during exercise.
• 💡Apply each mechanism to a sporting example, such as the leg muscles during running or breathing during cycling.
• 💡Learn the cardiac output equation and practise substituting values with correct units, for example cm³ per minute or dm³ per minute.
• 💡Link each receptor to the variable it detects: chemoreceptors to carbon dioxide and pH, baroreceptors to blood pressure.
• 💡Use precise directional language such as "vasodilation increases blood flow to working muscles" rather than vague phrases like "blood goes to the muscles".
• 💡Write blood pressure readings in the conventional systolic over diastolic form, for example 120/80 mmHg, and state the units.
• 💡When explaining exercise responses, link the rise in systolic pressure to increased cardiac output and the small change in diastolic pressure to vasodilation.
• 💡Use the terms "ventricular contraction" and "ventricular relaxation" rather than vague phrases such as "heart beating".
• 💡State the chain explicitly: venous return increases, end-diastolic volume increases, ventricular stretch increases, force of contraction increases, stroke volume increases.
• 💡Use the equation cardiac output equals heart rate multiplied by stroke volume to explain why cardiac output rises.
• 💡Link the law to exercise by naming the skeletal muscle pump and respiratory pump as mechanisms that raise venous return.
• 💡Define drift as a change during prolonged steady exercise, not at the start of exercise.
• 💡Explain the sequence: plasma volume falls, stroke volume falls, heart rate rises, cardiac output is maintained.
• 💡Use the cardiac output equation to show why heart rate must rise when stroke volume falls.
• 💡Learn the subtraction direction as arterial minus venous so the value is always positive.
• 💡Link a widening A-VO₂ diff to increased oxygen extraction by working muscles during exercise.
• 💡Quote a numerical example with units to show you understand the scale of the difference.
• 💡Compare responses using named variables such as heart rate, stroke volume and cardiac output rather than saying fitness differs.
• 💡Link variation to at least two specific factors, for example training status and temperature.
• 💡Use correct units when quoting values so comparisons are meaningful.
• 💡Compare trained and untrained values directly, naming the variable and the direction of the difference.
• 💡Link each difference to a cardiovascular adaptation, such as a larger stroke volume or a lower resting heart rate.
• 💡Use the relationship cardiac output = heart rate × stroke volume to explain why resting cardiac output can be similar.
• 💡Check whether the question asks about rest, submaximal exercise or maximal exercise, because the pattern of differences changes.
• 💡Name the body system before stating the adaptation, so the link is clear.
• 💡Explain how each adaptation contributes to the training effect, such as increased stroke volume raising cardiac output.
• 💡Use correct terminology, including stroke volume, cardiac output, mitochondria and maximum oxygen uptake.
• 💡Avoid listing adaptations without linking them to improved aerobic performance.
• 💡Always use specific anatomical terminology (e.g. 'sinoatrial node', 'atrioventricular node', 'bundle of His', 'Purkinje fibres') rather than vague terms like 'pacemaker' or 'nerves'.
• 💡When explaining responses or adaptations, link the change to its effect on performance (e.g. 'increased stroke volume leads to greater oxygen delivery, delaying fatigue').
• 💡For calculation questions, show your working clearly and include units (L/min or mL/min) to secure full marks.

• Misunderstanding: students treat health and fitness as identical. Correction: health is the overall state of well-being and absence of disease, while fitness is the ability to meet environmental demands.
• Misunderstanding: students think only vigorous sport improves cardiovascular health. Correction: moderate regular activity also produces significant health benefits, such as lowered blood pressure.
• Misunderstanding: students state that maximum heart rate increases with training. Correction: maximum heart rate remains relatively unchanged (220 minus age); it is stroke volume and cardiac output that increase.
• Misunderstanding: all cholesterol is harmful. Correction: cholesterol is needed for cell membranes and hormone production; the balance of low-density and high-density lipoprotein matters for cardiovascular health.
• Misunderstanding: high blood pressure only affects the heart. Correction: it also damages arteries, the brain and kidneys, and raises stroke risk.
• Misunderstanding: a stroke is the same as a heart attack. Correction: a heart attack affects cardiac muscle when coronary blood flow is blocked; a stroke affects the brain when cerebral blood flow is interrupted.
• Misunderstanding: heart disease is only caused by genetics. Correction: lifestyle factors such as diet, inactivity and smoking interact with genetics to influence risk.
• Misunderstanding: cardiac output is the same as heart rate. Correction: cardiac output is heart rate multiplied by stroke volume, so it depends on both.
• Misunderstanding: trained individuals always have a higher cardiac output at rest. Correction: resting cardiac output is similar; the difference is a lower resting heart rate and larger stroke volume in trained individuals.
• Misunderstanding: stroke volume cannot change with training. Correction: endurance training increases stroke volume, which raises maximal cardiac output.
• Misunderstanding: sub-maximal exercise requires the same heart rate in trained and untrained individuals. Correction: trained individuals reach a given cardiac output at a lower heart rate.
• Thinking only nerves control the heart: the correction is that hormones such as adrenaline and chemical stimuli detected by chemoreceptors also regulate the response.
• Confusing the roles of the two autonomic branches: the correction is that sympathetic activity speeds the heart while parasympathetic (vagal) activity slows it.
• Believing chemoreceptors detect only oxygen: the correction is that they are most sensitive to rises in carbon dioxide and falls in pH, with oxygen also monitored.
• Assuming heart rate rises only after exercise starts: the correction is that proprioceptor and cortical input can raise it before activity begins.
• Defining anticipatory rise as the rise during exercise: the correction is that it happens before activity begins, driven by anticipation.
• Attributing it only to adrenaline: the correction is that neural input from the cortex and limbic system to the medulla is the primary trigger, with hormones reinforcing it.
• Confusing it with the oxygen deficit: the correction is that anticipatory rise helps reduce the oxygen deficit but is not the same thing.
• Ignoring the role of the parasympathetic system: the correction is that vagal tone decreases as part of the response.
• Thinking vasoconstriction occurs in working muscles: correct this by stating that working muscles vasodilate and non-essential organs vasoconstrict.
• Confusing vasodilation with increased heart rate: correct this by explaining that vasodilation changes vessel diameter and local flow, not the rate of contraction.
• Believing blood is created or destroyed during shunting: correct this by stating that the same cardiac output is redistributed, not increased in total by shunting alone.
• Ignoring the role of the vasomotor centre: correct this by naming the medulla oblongata as the control centre for sympathetic outflow.
• Thinking the AV node is the pacemaker: correct this by stating the SA node sets the rhythm and the AV node delays the impulse.
• Believing the impulse passes directly from atria to ventricles without a delay: correct this by explaining the AV nodal delay allows complete atrial emptying.
• Confusing the bundle of His with the AV node: correct this by describing the bundle of His as the pathway from the AV node into the ventricular septum.
• Stating that Purkinje fibres initiate the heartbeat: correct this by saying they conduct the impulse to ventricular muscle, which then contracts.
• Thinking the sympathetic division slows the heart: the sympathetic division speeds the heart up, while the parasympathetic division slows it down.
• Believing the two divisions work one at a time: they are antagonistic and both exert some influence, with the balance shifting with exercise intensity.
• Confusing the autonomic control of heart rate with voluntary control of skeletal muscle: cardiac muscle is controlled involuntarily through the autonomic nervous system.
• Assuming parasympathetic activity stops completely during exercise: it is reduced rather than necessarily absent, and it returns to dominance during recovery.
• Treating carbon dioxide as a fuel for exercise: it is a waste product of aerobic respiration that acts as a stimulus for cardiovascular adjustment.
• Confusing chemoreceptors with baroreceptors: chemoreceptors detect chemical changes such as carbon dioxide and pH, while baroreceptors detect changes in blood pressure.
• Assuming carbon dioxide only affects breathing: it also drives cardiovascular changes, including increased heart rate and local vasodilation in active muscle.
• Forgetting the direction of the pH change: increased carbon dioxide is associated with a fall in pH, not a rise.
• Confusing chemoreceptors with baroreceptors: chemoreceptors respond to blood chemistry such as carbon dioxide and pH, whereas baroreceptors respond to stretch caused by blood pressure changes.
• Thinking proprioceptors detect blood pressure: proprioceptors detect movement and position of muscles and joints, not pressure inside vessels.
• Believing receptors themselves raise heart rate: receptors only detect and send information; the medulla oblongata and autonomic nervous system produce the response.
• Assuming only one receptor type operates during exercise: chemoreceptors, proprioceptors and baroreceptors all contribute information during physical activity.
• Mixing up the stimulus for each receptor: chemoreceptors detect chemical changes, proprioceptors detect movement, and baroreceptors detect stretch from pressure.
• Thinking baroreceptors detect carbon dioxide: baroreceptors detect stretch of vessel walls, while chemoreceptors detect blood gases and pH.
• Believing proprioceptors are only in the heart: proprioceptors are located in muscles, tendons and joints and detect body movement.
• Stating that receptors directly change heart rate: receptors send information to the medulla oblongata, which then alters autonomic nerve activity.
• Thinking that all oxygen is carried dissolved in plasma: most oxygen is bound to haemoglobin, and only a small fraction dissolves in plasma.
• Believing that oxygen is actively pumped by haemoglobin: oxygen moves by diffusion down partial pressure gradients, and haemoglobin binds and releases it according to those gradients.
• Confusing oxyhaemoglobin with haemoglobin: oxyhaemoglobin is the combined form produced when oxygen binds to haemoglobin at the lungs.
• Assuming oxygen is released at the lungs rather than the tissues: oxygen binds at the lungs and dissociates at the respiring tissues.
• Thinking haemoglobin is found in plasma: haemoglobin is contained within red blood cells.
• Believing haemoglobin binds oxygen irreversibly: the binding is reversible, which allows oxygen to be released at the tissues.
• Stating that each haemoglobin molecule binds one oxygen molecule: it can bind up to four oxygen molecules.
• Assuming haemoglobin releases oxygen at the lungs: it loads oxygen at the lungs and releases it at respiring tissues.
• Thinking myoglobin is found in red blood cells: it is found in skeletal muscle, whereas haemoglobin is the pigment inside red blood cells.
• Believing myoglobin carries four oxygen molecules like haemoglobin: myoglobin has one haem group and therefore binds one molecule of O₂.
• Assuming myoglobin releases oxygen only when partial pressure of oxygen is high: its high affinity means it loads oxygen at low partial pressure and releases it when tissue partial pressure falls further during contraction.
• Confusing myoglobin with mitochondria: myoglobin stores and transports oxygen, while mitochondria use that oxygen in aerobic respiration.
• Reversing the axes: percentage saturation of haemoglobin with oxygen is on the y-axis and partial pressure of oxygen is on the x-axis.
• Describing the curve as a straight line: it is sigmoid because cooperative binding makes the middle section steeper.
• Confusing a rightward shift with reduced oxygen release: a rightward (Bohr) shift means haemoglobin releases more oxygen to tissues at the same pO₂.
• Thinking the Bohr shift occurs because haemoglobin has a lower affinity at high pO₂: the shift is caused by increased carbon dioxide, increased temperature and decreased pH in active muscle.
• Thinking the Bohr shift means haemoglobin carries more oxygen: it actually means haemoglobin releases oxygen more readily at the tissues.
• Confusing a rightward shift with a leftward shift: a rightward shift shows reduced affinity and easier unloading.
• Believing carbon dioxide directly displaces oxygen: the effect works mainly through the fall in pH caused by carbon dioxide.
• Assuming the shift changes the maximum saturation of haemoglobin: it changes the position of the curve, not the maximum achievable saturation.
• Thinking veins have no role in circulation because they are low pressure: their valves, muscle pump and respiratory pump are essential to venous return.
• Confusing venous return with cardiac output: venous return is blood coming back to the heart, while cardiac output is blood pumped out.
• Believing the skeletal muscle pump works when muscles relax: it is muscle contraction that compresses the veins.
• Assuming valves push blood: valves only prevent backflow; the pressure gradient and pumps provide the movement.
• Thinking cardiac output is only heart rate; correction: cardiac output is heart rate multiplied by stroke volume, so both must be considered.
• Confusing vasodilation with vasoconstriction; correction: vasodilation widens vessels to increase blood flow to working muscles, while vasoconstriction narrows vessels to reduce flow elsewhere.
• Believing blood is redirected by the heart alone; correction: the vascular shunt depends on arterioles changing diameter under nervous and local control.
• Assuming venous return relies only on the heart; correction: the skeletal muscle pump, respiratory pump and venous valves all assist return of blood to the right atrium.
• Reversing the definitions; correction: systolic pressure occurs during ventricular contraction, while diastolic pressure occurs during ventricular relaxation.
• Believing both values rise equally during exercise; correction: systolic pressure rises markedly, while diastolic pressure usually stays similar or falls slightly.
• Thinking diastolic pressure is the pressure when the heart stops; correction: it is the pressure during the relaxation and filling phase of the cardiac cycle.
• Ignoring units; correction: blood pressure is measured in millimetres of mercury, written as mmHg.
• Thinking Starling's law increases heart rate: it changes the force of contraction and stroke volume, while heart rate is influenced separately.
• Believing stroke volume can rise indefinitely: excessive ventricular filling eventually reduces the effectiveness of contraction.
• Confusing venous return with cardiac output: venous return is the blood returning to the heart, whereas cardiac output is the volume the heart pumps out per minute.
• Assuming the law applies to atria only: the key stretch and force relationship is described for ventricular muscle.
• Thinking cardiac output falls during drift: cardiac output is maintained while heart rate rises and stroke volume falls.
• Believing heart rate falls during drift: heart rate gradually increases as stroke volume decreases.
• Confusing drift with the initial anticipatory rise in heart rate before exercise: drift develops over prolonged steady exercise.
• Assuming drift only occurs in trained athletes: it can occur in any performer during prolonged exercise, especially in heat.
• Reversing the subtraction: the error is taking arterial content away from venous content; the correction is arterial minus venous, so the value is positive.
• Confusing A-VO₂ diff with cardiac output: the error is treating the difference as a volume pumped per minute; the correction is that it is an oxygen content difference per 100 cm³ of blood.
• Assuming the difference stays constant: the error is thinking extraction is fixed; the correction is that it increases during exercise as muscles take up more oxygen.
• Mixing up which vessel carries more oxygen: the error is saying venous blood has more oxygen; the correction is that arterial blood has the higher oxygen content.
• Treating one response as universal: the error is assuming everyone shows the same heart-rate rise; the correction is that training status and individual factors change the response.
• Confusing cardiac output with heart rate: the error is using the terms interchangeably; the correction is that cardiac output is heart rate multiplied by stroke volume.
• Ignoring recovery: the error is only comparing peak values; the correction is that the speed of return to resting values also varies between individuals.
• Assuming a higher heart rate always means poorer fitness: the error is judging fitness from one reading; the correction is that the same heart rate can reflect different workloads, conditions and individuals.
• Assuming trained individuals always have a higher resting cardiac output: correction, resting cardiac output is often similar because a lower resting heart rate can balance a larger stroke volume.
• Confusing heart rate with cardiac output: correction, cardiac output is the product of heart rate and stroke volume, so a lower heart rate does not automatically mean a lower cardiac output.
• Believing stroke volume is fixed: correction, stroke volume increases with training because the heart fills more and contracts more forcefully.
• Thinking untrained individuals have a higher maximum oxygen uptake: correction, trained individuals generally achieve a higher maximum oxygen uptake because they can deliver and use more oxygen.
• Listing only cardiovascular changes: correction, the training effect also involves respiratory and muscular adaptations such as stronger respiratory muscles and more mitochondria.
• Confusing an acute response with a chronic adaptation: correction, an acute response occurs during or immediately after exercise, while an adaptation is a longer-term change from repeated training.
• Claiming lung volume increases without limit: correction, respiratory adaptations support greater oxygen uptake but are bounded by body size and training status.
• Assuming all training produces the same adaptations: correction, adaptations are specific to the type, intensity and duration of the training performed.
• Students often think the left side of the heart pumps deoxygenated blood to the lungs. Correction: the right side pumps deoxygenated blood to the lungs via the pulmonary artery; the left side pumps oxygenated blood to the body via the aorta.
• Many believe that heart rate increases solely because of adrenaline. Correction: heart rate is regulated by the cardiac accelerator and inhibitory centres in the medulla oblongata, which respond to chemoreceptors, baroreceptors and proprioceptors, using sympathetic and parasympathetic nerves.
• Students frequently state that blood pressure decreases during exercise. Correction: systolic blood pressure increases due to greater cardiac output, while diastolic pressure remains relatively stable or may decrease slightly due to vasodilation in working muscles.

1. 1Week 1, Days 1-2: Revise the structure of the heart and conduction system using diagrams and labelling exercises. Create flashcards for key terms.
2. 2Week 1, Days 3-4: Learn the cardiac cycle and vascular shunting. Practice explaining these in writing using correct terminology and pressure changes.
3. 3Week 1, Days 5-7: Study acute responses to exercise (heart rate, stroke volume, cardiac output, blood pressure, redistribution of blood flow) and complete past-paper questions.
4. 4Week 2, Days 1-3: Learn chronic adaptations to aerobic and anaerobic training. Compare adaptations and link to performance in different sports.
5. 5Week 2, Days 4-7: Complete a full topic test under timed conditions, mark using the mark scheme, and review examiner reports for common pitfalls.

• 📋Multiple-choice and short-answer questions (1-2 marks) testing definitions, e.g. 'Define cardiac output' or 'State the role of the AVN'.
• 📋Data analysis questions (3-4 marks) requiring interpretation of heart rate, stroke volume or blood pressure graphs, often asking students to calculate cardiac output or describe trends.
• 📋Extended writing questions (6-9 marks) asking students to explain or evaluate cardiovascular responses and adaptations to exercise, often applied to a specific sport or training programme.
• 📋Synoptic questions linking the cardiovascular system to the respiratory or energy systems, requiring integrated knowledge across topics.