Electrocardiogram (ECG or EKG)
Medically reviewed on May 19, 2018
An electrocardiogram records the electrical signals in your heart. It's a common test used to detect heart problems and monitor the heart's status in many situations. Electrocardiograms — also called ECGs or EKGs — are often done in a doctor's office, a clinic or a hospital room. And they've become standard equipment in operating rooms and ambulances.
An ECG is a noninvasive, painless test with quick results. During an ECG, sensors (electrodes) that can detect the electrical activity of your heart are attached to your chest and sometimes your limbs. These sensors are usually left on for just a few minutes.
Your doctor may discuss your results with you the same day as your electrocardiogram or at your next appointment.
Other types of heart rhythm monitoring
If you have a heart rhythm irregularity that tends to come and go, it may not be captured during the few minutes a standard ECG is recording. In this case your doctor may recommend another type of heart rhythm monitor.
- Holter monitor. A Holter monitor is a small, wearable device that records a continuous ECG, usually for 24 to 48 hours. Wires from electrodes on your chest go to a battery-operated recording device carried in your pocket or worn on a belt or shoulder strap. While you're wearing the monitor, you'll be able to go about your normal activities, as long as you keep the electrodes and device dry. In addition, your doctor will likely ask you to keep a diary of what you're doing when symptoms occur and the time. Your doctor will compare the diary with the electrical recordings to try to figure out the cause of your symptoms.
Event monitor. If your symptoms don't occur often, your doctor may suggest that you wear an 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. And you can wear it longer than a Holter monitor, typically 30 days.
With many event monitors, you activate them by pressing a record button when you have symptoms or a fast heart rate. Other monitors automatically sense abnormal heart rhythms and then start recording. You then send the ECG readings to your doctor through your phone. He or she uses the recorded electrical signals to look at your heart rhythm at the time of your symptoms.
- Stress test. If your symptoms occur most often during exercise, your doctor may ask you to walk on a treadmill or ride a stationary bike during an ECG. This is called a stress test. If you have a medical condition that makes it difficult for you to exercise, your doctor may inject you with a drug that mimics the effect of exercise on your heart.
- Implantable loop recorder. This is a continuous heart rhythm monitoring device. Like a Holter monitor, it continuously records your heart rhythms, but for a much longer time. An implantable loop recorder is inserted under the skin in the chest area during minor surgery and can be left in place for up to three years.
How it works
Each beat of your heart is triggered by an electrical impulse normally generated from special cells in the upper right chamber of your heart (pacemaker cells). An electrocardiogram records the timing and strength of these signals as they travel through your heart.
An electrocardiogram is also called a 12-lead EKG or 12-lead ECG because it gathers information from 12 different areas of the heart. These views are created by electrodes, typically 10, placed on the skin of your chest and sometimes your limbs. The electrical activity is recorded as waves on a graph, with different patterns corresponding to each electrical phase of your heartbeat.
A standard ECG can record an abnormal heart rhythm only if it happens during the test. Some abnormal heart rhythms come and go, so your doctor may have you undergo a different type of heart rhythm monitoring, such as with a Holter monitor, to help diagnose the cause of your symptoms.
An electrocardiogram monitors your heart rhythm for problems. Electrodes are taped to 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.
A Holter monitor uses electrodes and a recording device to track your heart's rhythm for 24 to 72 hours. Your doctor can print an electrocardiogram strip using the data on the recording device to see your heart's rhythm during the period you wore the monitor.
A wearable cardiac event monitor may be used to diagnose heart rhythm problems. This type of portable ECG device records heart activity only during episodes of abnormal heartbeat.
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 detect:
- Irregularities in your heart rhythm (arrhythmias)
- If blocked or narrowed arteries in your heart (coronary artery disease) are causing chest pain or a heart attack
- Structural problems with your heart's chambers
- A previous heart attack
- How well certain ongoing heart disease treatments, such as a pacemaker, are working
You may need a heart rhythm test if you experience any of the following signs and symptoms:
- Heart palpitations
- Rapid pulse
- Chest pain
- Shortness of breath
- Dizziness, lightheadedness or confusion
- 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 an early screening test, even if you have no symptoms.
An electrocardiogram is a safe procedure. You'll have no risk of getting an electrical shock during the test because the electrodes placed on your body don't emit electricity. They only record the electrical activity of your heart.
You may have minor discomfort, similar to removing a bandage, when the electrodes are removed. Rarely, a reaction to the electrode adhesive may cause redness or swelling where the patches were placed.
A stress test may lead to irregular heart rhythms and, rarely, a heart attack. These effects are brought on by the exercise or medication, not the ECG itself.
A Holter monitor may cause some skin irritation if you don't move the electrodes each day.
An implantable loop recorder has a slight risk of infection because it involves a minor surgical procedure. And some people may experience a reaction to the device that causes inflammation.
How you prepare
No special preparations are necessary for a standard electrocardiogram. Do tell your doctor about any medications and supplements you're taking because some can affect the results of your test.
What you can expect
During the ECG
An electrocardiogram can be done in a doctor's office or hospital and is often performed by a technician. You may be asked to change into a hospital gown. Then you'll lie on an examining table or bed.
Electrodes — typically 10 — will be attached to chest and sometimes to your limbs. The electrodes are sticky patches applied to help record the electrical activity of your heart. Each one has a wire attached to a monitor. 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.
You can breathe normally during the electrocardiogram. 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.
As you lie on the examination table or bed, the electrodes will record the impulses that make your heart beat. The impulses are recorded by a computer and displayed as waves on a monitor or printed on paper.
After the ECG
You can resume your normal activities after your electrocardiogram.
Your doctor will look at the waves recorded during your test to see if the impulses are traveling normally. He or she will be able to tell you the results of your ECG the same day it's performed 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 look for a consistent, even heart rhythm and a heart rate between 50 and 100 beats a minute. Having a faster, slower or irregular heartbeat provides clues about your heart health, 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 abnormalities on your ECG, he or she may order additional tests to see if treatment is necessary.