One of the most common cardiac evaluation tools is an electrocardiogram, which is a simple, painless test that records the heart's electrical activity. An electrocardiogram is called an EKG or ECG or sometimes a 12-lead EKG or 12-lead ECG because the electrical activity of the heart is most often recorded from 12 different places on the body at the same time.

To understand this test, it helps to understand how the heart works. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the signal causes the heart to contract and pump blood. The process repeats with each new heartbeat. The heart's electrical signals set the rhythm of the heartbeat. An EKG shows how fast your heart is beating, whether the rhythm of your heartbeat is steady or irregular, and the strength and timing of electrical signals as they pass through each part of your heart. This test is used to detect and evaluate many heart problems, such as heart attack, arrhythmia, and heart failure. EKG results also can suggest other disorders that affect heart function.

Your doctor may recommend an electrocardiogram (EKG) if you have signs or symptoms that suggest a heart problem. Examples of such signs and symptoms include:

  • Chest pain
  • Heart pounding, racing, or fluttering, or the sense that your heart is beating unevenly
  • Problems breathing
  • Feeling tired and weak
  • Unusual heart sounds when your doctor listens to your heartbeat

You may have an EKG so your doctor can check how well heart medicine or a medical device, such as a pacemaker, is working. The test also may be used for routine screening before major surgery.

How to prepare for an electrocardiogram

No special preparation is needed for an electrocardiogram (EKG). Before the test, let your doctor know what medicines you're taking. Some medicines can affect EKG results.

The illustration shows the standard setup for an EKG. In figure A, a normal heart rhythm recording shows the electrical pattern of a regular heartbeat. In figure B, a patient lies in a bed with EKG electrodes attached to his chest, upper arms, and legs. A nurse watches the painless procedure.

What To Expect During an Electrocardiogram?

A technician attaches soft, sticky patches called electrodes to the skin of your chest, arms, and legs. The patches are about the size of a quarter. Typically, 12 patches are attached to detect your heart's electrical activity from many angles. To help the patches stick, the technician may have to shave areas of your skin. After the patches are placed on your skin, you lie still on a table while the patches detect your heart's electrical signals. A machine records these signals on graph paper or displays them on a screen. The entire test takes about 10 minutes.