Why it's done

A pacemaker is implanted to help control your heartbeat. Your doctor may recommend a temporary pacemaker when you have a slow heartbeat (bradycardia) after a heart attack, surgery or medication overdose but your heartbeat is otherwise expected to recover. A pacemaker may be implanted permanently to correct a chronic slow or irregular heartbeat or to help treat heart failure.

How your heart beats

The heart is a muscular, fist-sized pump with four chambers, two on the left side and two on the right. The upper chambers (right and left atria) and the lower chambers (right and left ventricles) work with your heart's electrical system to keep your heart beating at an appropriate rate — usually 60 to 100 beats a minute for adults at rest.

Your heart's electrical system controls your heartbeat, beginning in a group of cells at the top of the heart (sinus node) and spreading to the bottom, causing it to contract and pump blood. Aging, heart muscle damage from a heart attack, some medications and certain genetic conditions can cause an abnormal heart rhythm.

What a pacemaker does

Pacemakers work only when needed. If your heartbeat is too slow (bradycardia), the pacemaker sends electrical signals to your heart to correct the beat.

Some newer pacemakers also have sensors that detect body motion or breathing rate and signal the devices to increase heart rate during exercise, as needed.

A pacemaker has two parts:

• Pulse generator. This small metal container houses a battery and the electrical circuitry that controls the rate of electrical pulses sent to the heart.
• Leads (electrodes). One to three flexible, insulated wires are each placed in one or more chambers of the heart and deliver the electrical pulses to adjust the heart rate. However, some newer pacemakers don't require leads. These devices, called leadless pacemakers, are implanted directly into the heart muscle.