Electrocardiogram (EKG)


What Is It?

An electrocardiogram (EKG) is a painless recording of the heart’s electrical activity. This electrical activity is detected by small metal electrodes, which are placed on the patient’s wrists, ankles and chest. Then the electrical signals are carried from the electrodes through wires to the EKG machine, which transforms the signals into standard patterns or waves. Different waves represent different areas of your heart through which tiny electrical currents flow, causing the heart muscles to contract and relax. Briefly, the P wave represents the current in the atria, or the upper chambers of the heart; the QRS complex, the current in the ventricles (the lower heart chambers); and the T wave, the heart’s brief “rest period” as it repolarizes (recharges electrically) between heartbeats.

The paper tracing of EKG waves shows the heart rate and heart rhythm, and can give important clues about damage to the heart muscle or irritation of the membrane around the heart (pericardium).

In most cases, a basic EKG takes about five to 10 minutes. It can be performed in a doctor’s office, in a laboratory or in a hospital bed.

What It’s Used For

An EKG can be used to evaluate patients with chest pain, patients thought to be having a heart attack, and patients suspected of having coronary artery disease or a cardiac arrhythmia. It also can help to diagnose pericarditis (an inflammation of the membrane around the heart), Pulmonary embolism (a blood clot blocking blood flow in a lung), abnormal blood levels of potassium or calcium, or overdoses of certain medications.

An EKG sometimes is performed as part of a regular physical examination or as a screening test in people at high risk of heart problems, including people with high blood pressure (hypertension), High cholesterol, diabetes, a strong family history of heart problems, and people who smoke. The EKG sometimes will show the patient has coronary artery disease even if there are no symptoms.

During surgery, a continuous EKG tracing helps to monitor the functioning of the patient’s heart.


In most cases, no special preparation is necessary. However, if you are taking any medications, be sure to tell the EKG technician about these drugs beforehand. This is because certain medicines have effects on the heart that can influence the appearance of an EKG tracing.

Since you will be asked to remove any bracelets and long necklaces during your EKG, you may wish to leave these items at home. Also, it would be helpful to wear a shirt that can be unbuttoned easily.

How It’s Done

You will need to expose the skin above your ankles, wrists and chest. If you need to undress, you will be given a gown. You will lie down on an examination table, and an EKG technician will clean portions of your arms, legs and chest to remove excess skin oils and sweat. In certain male patients, a small area of chest hair may need to be shaved.

Next, about 10 small metal electrodes will be attached to various parts of your body, including one on each arm and leg, six across the left side of the chest and, at times, one or more at other sites on the chest, neck and back. The electrodes are attached with sticky pads while you are lying down.

Once the electrodes are attached, you only need to relax as your EKG is recorded. You won’t feel anything. Breathe normally, avoid talking, and don’t make any unnecessary motions. When your EKG is done, the technician will remove all the electrodes and you will be allowed to dress. Ask the technician if you need to speak with your doctor before you leave.


Depending on the reason that your doctor ordered the EKG, he or she may ask to see it immediately. If it is being done as part of a routine physical or preoperative evaluation, then ask the technician whether your doctor will notify you of the result, or whether your will need to call the doctor’s office.


An EKG is considered to be a safe, routine diagnostic procedure, with no harmful side effects.

When To Call A Professional

Since harmful side effects are not expected, patients typically need to call their doctors only for EKG results.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.