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What Is an Electrocardiogram?

An electrocardiogram (e-lek-tro-KAR-de-o-gram), also called an EKG or ECG, is a simple, painless test that records the heart's electrical activity. 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. For more detailed information and animations, go to the Health Topics How the Heart Works article.

An EKG shows:

  • How fast your heart is beating
  • Whether the rhythm of your heartbeat is steady or irregular
  • The strength and timing of electrical signals as they pass through each part of your heart

Doctors use EKGs to detect and study many heart problems, such as heart attacks, arrhythmias (ah-RITH-me-ahs), and heart failure. The test's results also can suggest other disorders that affect heart function.




Other Names for an Electrocardiogram

An electrocardiogram also is called an EKG or ECG. Sometimes the test is called a 12-lead EKG or 12-lead ECG. This is because the heart's electrical activity most often is recorded from 12 different places on the body at the same time.




Who Needs an Electrocardiogram?

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
  • Breathing problems
  • Tiredness and weakness
  • Unusual heart sounds when your doctor listens to your heartbeat

You may need to have more than one EKG so your doctor can diagnose certain heart conditions.

An EKG also may be done as part of a routine health exam. The test can screen for early heart disease that has no symptoms. Your doctor is more likely to look for early heart disease if your mother, father, brother, or sister had heart disease—especially early in life.

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.

Your doctor also may use EKG results to help plan your treatment for a heart condition.




What To Expect Before an Electrocardiogram

You don't need to take any special steps before having an electrocardiogram (EKG). However, tell your doctor or his or her staff about the medicines you're taking. Some medicines can affect EKG results.




What To Expect During an Electrocardiogram

An electrocardiogram (EKG) is painless and harmless. A nurse or technician will attach soft, sticky patches called electrodes to the skin of your chest, arms, and legs. The patches are about the size of a quarter.

Often, 12 patches are attached to your body. This helps detect your heart's electrical activity from many areas at the same time. The nurse may have to shave areas of your skin to help the patches stick.

After the patches are placed on your skin, you'll lie still on a table while the patches detect your heart's electrical signals. A machine will record these signals on graph paper or display them on a screen.

The entire test will take about 10 minutes.

EKG

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

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

Special Types of Electrocardiogram

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

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 only for a few minutes a day or only while you exercise.

Doctors use special EKGs, such as stress tests and Holter and event monitors, 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 an EKG is done. If you can't exercise, you'll be given medicine to make your heart work hard and beat fast.

For more information, go to the Health Topics Stress Testing article.

Holter and Event Monitors

Holter and event monitors are small, portable devices. They record your heart's electrical activity while you do your normal daily activities. A Holter monitor records your heart's electrical activity for a full 24- or 48-hour period.

An event monitor records your heart's electrical activity only 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, go to the Health Topics Holter and Event Monitors article.




What To Expect After an Electrocardiogram

After an electrocardiogram (EKG), the nurse or technician will remove the electrodes (soft patches) from your skin. You may develop a rash or redness where the EKG patches were attached. This mild rash often goes away without treatment.

You usually can go back to your normal daily routine after an EKG.




What Does an Electrocardiogram Show?

Many heart problems change the heart's electrical activity in distinct ways. An electrocardiogram (EKG) can help detect these heart problems.

EKG recordings can help doctors diagnose heart attacks that are in progress or have happened in the past. This is especially true if doctors can compare a current EKG recording to an older one.

An EKG also can show:

An EKG can reveal whether the heartbeat starts in the correct place in the heart. The test also shows how long it takes for electrical signals to travel through the heart. Delays in signal travel time may suggest heart block or long QT syndrome.




What Are the Risks of an Electrocardiogram?

An electrocardiogram (EKG) has no serious risks. It's a harmless, painless test that detects the heart's electrical activity. EKGs don't give off electrical charges, such as shocks.

You may develop a mild rash where the electrodes (soft patches) were attached. This rash often goes away without treatment.




Links to Other Information About Electrocardiograms

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October 01, 2010 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.