An electrocardiogram (ECG or EKG) records the electrical signal from your heart to check for different heart conditions. Electrodes are placed on your chest to record your heart's electrical signals, which cause your heart to beat. The signals are shown as waves on an attached computer monitor or printer.
An electrocardiogram records the electrical signals in your heart. It's a common and painless test used to quickly detect heart problems and monitor your heart's health.
Electrocardiograms — also called ECGs or EKGs — are often done in a doctor's office, a clinic or a hospital room. ECG machines are standard equipment in operating rooms and ambulances. Some personal devices, such as smart watches, offer ECG monitoring. Ask your doctor if this is an option for you.
Products & Services
Why it's done
An electrocardiogram is a painless, noninvasive way to help diagnose many common heart problems in people of all ages. Your doctor may use an electrocardiogram to determine or detect:
- Abnormal heart rhythm (arrhythmias)
- If blocked or narrowed arteries in your heart (coronary artery disease) are causing chest pain or a heart attack
- Whether you have had a previous heart attack
- How well certain heart disease treatments, such as a pacemaker, are working
You may need an ECG if you have any of the following signs and symptoms:
- Chest pain
- Dizziness, lightheadedness or confusion
- Heart palpitations
- Rapid pulse
- Shortness of breath
- Weakness, fatigue or a decline in ability to exercise
The American Heart Association doesn't recommend using electrocardiograms to assess adults at low risk who don't have symptoms. But if you have a family history of heart disease, your doctor may suggest an electrocardiogram as a screening test, even if you have no symptoms.
If your symptoms tend to come and go, they may not be captured during a standard ECG recording. In this case your doctor may recommend remote or continuous ECG monitoring. There are several different types.
- Holter monitor. A Holter monitor is a small, wearable device that records a continuous ECG, usually for 24 to 48 hours.
- Event monitor. This portable device is similar to a Holter monitor, but it records only at certain times for a few minutes at a time. You can wear it longer than a Holter monitor, typically 30 days. You generally push a button when you feel symptoms. Some devices automatically record when an abnormal rhythm is detected.
ECG on medical helicopter
A patient receives an ECG while on a helicopter for medical transport.
An electrocardiogram is a safe procedure. There is no risk of electrical shock during the test because the electrodes used do not produce electricity. The electrodes only record the electrical activity of your heart.
You may have minor discomfort, similar to removing a bandage, when the electrodes are removed. Some people develop a slight rash where the patches were placed.
How you prepare
No special preparations are necessary for a standard electrocardiogram. Tell your doctor about any medications and supplements you take. These can often affect the results of your test.
What you can expect
An electrocardiogram can be done in a doctor's office or hospital and is often done by a nurse or technician.
You may be asked to change into a hospital gown. If you have hair on the parts of your body where the electrodes will be placed, the technician may shave the hair so that the patches stick.
Once you're ready, you'll be asked to lie on an examining table or bed.
During an ECG, up to 12 sensors (electrodes) will be attached to your chest and limbs. The electrodes are sticky patches with wires that connect to a monitor. They record the electrical signals that make your heart beat. A computer records the information and displays it as waves on a monitor or on paper.
You can breathe normally during the test, but you will need to lie still. Make sure you're warm and ready to lie still. Moving, talking or shivering may distort the test results. A standard ECG takes a few minutes.
You can resume your normal activities after your electrocardiogram.
Your doctor may discuss your results with you the same day as your electrocardiogram or at your next appointment.
If your electrocardiogram is normal, you may not need any other tests. If the results show an abnormality with your heart, you may need another ECG or other diagnostic tests, such as an echocardiogram. Treatment depends on what's causing your signs and symptoms.
Your doctor will review the information recorded by the ECG machine and look for any problems with your heart, including:
- Heart rate. Normally, heart rate can be measured by checking your pulse. An ECG may be helpful if your pulse is difficult to feel or too fast or too irregular to count accurately. An ECG can help your doctor identify an unusually fast heart rate (tachycardia) or an unusually slow heart rate (bradycardia).
- Heart rhythm. An ECG can show heart rhythm irregularities (arrhythmias). These conditions may occur when any part of the heart's electrical system malfunctions. In other cases, medications, such as beta blockers, cocaine, amphetamines, and over-the-counter cold and allergy drugs, can trigger arrhythmias.
- Heart attack. An ECG can show evidence of a previous heart attack or one that's in progress. The patterns on the ECG may indicate which part of your heart has been damaged, as well as the extent of the damage.
- Inadequate blood and oxygen supply to the heart. An ECG done while you're having symptoms can help your doctor determine whether chest pain is caused by reduced blood flow to the heart muscle, such as with the chest pain of unstable angina.
- Structural abnormalities. An ECG can provide clues about enlargement of the chambers or walls of the heart, heart defects and other heart problems.
If your doctor finds any problems on your ECG, he or she may order additional tests to see if treatment is necessary.
Explore Mayo Clinic studies of tests and procedures to help prevent, detect, treat or manage conditions.