Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

A pacemaker is an implanted device that regulates your heartbeat electronically. It monitors your heart's rhythm and, when necessary, it generates a painless electric impulse that triggers a heartbeat.

Your pacemaker is programmed to meet the needs of your heart. Early pacemakers were implanted to treat bradycardia, an abnormally slow heartbeat. Now pacemakers can be programmed to treat a variety of heart problems, including heart failure.

The electronic control center of your pacemaker the part that is programmed by your doctor is called the pulse generator. The pulse generator is a unit encased in titanium that usually is placed under the skin below your collarbone. In most cases, the unit is small, often weighing less than 30 grams (about 1 ounce). A lithium iodide battery inside the generator lasts 5 to 12 years, with an average of 7 to 8 years. Other sophisticated electronic components are responsible for:

  • Sensing your natural heartbeat

  • Generating an electrical impulse, called a pacing pulse, according to how the unit is programmed

  • Keeping an electronic record of your heartbeat and your pacemaker's activity

The pulse generator is attached to one or more wires called leads. These are threaded through large blood vessels in your upper chest into your heart. At the ends of the leads are small electrodes that attach to the inner surface of your heart. These electrodes pick up your heart's natural electric signals. The pacing pulse from the pulse generator travels along the leads to your heart muscle.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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