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An electrocardiogram (ECG) is a test that records the electrical activity of the heart.
You will be asked to lie down. The health care provider will clean several areas on your arms, legs, and chest, and then will attach small patches called electrodes to those areas. It may be necessary to shave or clip some hair so the patches stick to the skin. The number of patches used may vary.
The patches are connected by wires to a machine that turns the heart's electrical signals into wavy lines, which are often printed on paper. The doctor reviews the test results.
You will need to remain still during the procedure. The health care provider may also ask you to hold your breath for a few seconds as the test is being done.
It is important to be relaxed and warm during an ECG recording because any movement, including shivering, can alter the results.
Sometimes this test is done while you are exercising or under light stress to look for changes in the heart. This type of ECG is often called a stress test.
Make sure your health care provider knows about all the medicines you are taking. Some drugs can interfere with test results.
Do not exercise or drink cold water immediately before an ECG because these actions may cause false results.
An ECG is painless. No electricity is sent through the body. The electrodes may feel cold when first applied. In rare cases, some people may develop a rash or irritation where the patches were placed.
An ECG is used to measure:
An ECG is often the first test done to determine whether a person has heart disease. Your doctor may order this test if:
There is no reason for healthy people to have yearly ECG tests.
Normal test results include:
Abnormal ECG results may be a sign of:
Some heart problems that can lead to changes on an ECG test include:
There are no risks.
The accuracy of the ECG depends on the condition being tested. A heart problem may not always show up on the ECG. Some heart conditions never produce any specific ECG changes.
Ganz L. Electrocardiography. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 54.