What Happens During an Electrocardiogram?

An electrocardiogram (EKG) is painless and harmless. 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.

Special Types of Electrocardiogram

The standard EKG described above, called a resting 12-lead EKG, records only seconds of heart activity at a time. It will show a heart problem only if the problem is present during the time that the test is run.

Many heart problems are present all the time, and a resting 12-lead EKG will detect them. But some heart problems, like those related to an irregular heartbeat, can come and go. They may occur for only a few minutes out of the day or only while you exercise.

Special EKGs, such as stress tests and Holter and event monitors, are used to help diagnose these kinds of problems.

Stress Test

Some heart problems are easier to diagnose when your heart is working hard and beating fast. During stress testing, you exercise to make your heart work hard and beat fast while your heart's electrical activity is recorded. If you're not able to exercise, you're given medicine to make your heart work hard and beat fast.

For more information, see the Diseases and Conditions Index article on Stress Testing.

Holter and Event Monitors

Holter and event monitors are small, portable devices. They record your heart’s activity while you do your normal daily activities. A Holter monitor records the heart’s electrical activity for a full 24-hour period or longer.

An event monitor only records your heart’s electrical activity at certain times while you’re wearing it. For many event monitors, you push a button to start the monitor when you feel symptoms. Other event monitors start automatically when they sense abnormal heart rhythms.

For more information, see the Diseases and Conditions Index article on Holter and Event Monitors.