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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.

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Electrocardiogram Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Electrocardiogram, visit www.clinicaltrials.gov.


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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.