The heart and blood vessels: The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate.

The idea

Your resting heart rate is set by a small group of specialised cells in the wall of the right atrium. These cells act as a natural pacemaker: they produce regular electrical impulses that spread through the heart muscle and make it contract rhythmically. The rate is adjusted by the nervous system and by hormones such as adrenaline, but the basic rhythm originates in the right atrium. If this natural pacemaker or the electrical pathway becomes faulty, the heart may beat too slowly, too quickly or irregularly. An artificial pacemaker is an electrical device implanted under the skin, usually near the collarbone, with leads that carry small electrical impulses to the heart. These impulses stimulate the heart to contract at a suitable rate, correcting the irregularity. You should be able to state the location and role of the natural pacemaker and explain what an artificial pacemaker does.

What earns the marks

• States that the natural resting heart rate is controlled by a group of cells in the right atrium.
• Explains that these cells act as a pacemaker by producing electrical impulses that cause the heart muscle to contract rhythmically.
• Describes an artificial pacemaker as an electrical device that corrects irregularities in heart rate.
• Explains that an artificial pacemaker sends electrical impulses to the heart to stimulate contractions at an appropriate rate.
• Recognises that a faulty natural pacemaker can cause the heart to beat too slowly, too quickly or irregularly.
• Distinguishes the natural pacemaker in the right atrium from an artificial pacemaker implanted as a device.

Common mistakes and how to put them right

• Saying the pacemaker cells are in the left atrium.

  Put it right: The natural pacemaker cells are located in the right atrium.

• Confusing the natural pacemaker with an artificial pacemaker.

  Put it right: The natural pacemaker is a group of cells, while an artificial pacemaker is an implanted electrical device.

• Claiming that an artificial pacemaker supplies oxygen or blood to the heart.

  Put it right: It supplies electrical impulses that stimulate the heart muscle to contract at a suitable rate.

Exam tips

• Name the right atrium explicitly when describing the natural pacemaker, because the location is part of the required knowledge.
• Use the phrase electrical impulses for both the natural pacemaker and the artificial pacemaker to show the shared mechanism.
• When explaining an artificial pacemaker, state what it corrects and how it does so, for example it corrects an irregular heart rate by sending electrical impulses to the heart.
• Avoid describing the pacemaker as a pump; it controls the rhythm of contraction rather than moving blood itself.