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What is an electrocardiogram?

An electrocardiogram (ECG or EKG) is one of the simplest and fastest tests used to evaluate the heart. Electrodes (small, plastic patches that stick to the skin) are placed at certain spots on the chest, arms, and legs. The electrodes are connected to an ECG machine by lead wires. The electrical activity of the heart is then measured, interpreted, and printed out. No electricity is sent into the body.

Natural electrical impulses coordinate contractions of the different parts of the heart to keep blood flowing the way it should. An ECG records these impulses to show how fast the heart is beating, the rhythm of the heart beats (steady or irregular), and the timing of the electrical impulses as they move through the different parts of the heart. Changes in an ECG can be a sign of many heart-related conditions.

Healthcare provider monitoring patient having electrocardiogram while reclining on exam table.

Why might I need an electrocardiogram?

Some reasons your healthcare provider may request an ECG include:

  • To look for the cause of chest pain

  • To evaluate problems that may be heart-related, such as severe tiredness (fatigue), shortness of breath, dizziness, or fainting

  • To identify irregular heartbeats

  • To help assess the overall health of the heart before procedures, such as surgery; after treatment for a heart attack (myocardial infarction), endocarditis (inflammation or infection of one or more of the heart valves), or other condition; or after heart surgery or cardiac catheterization

  • To see how an implanted pacemaker is working

  • To find out how well certain heart medicines are working

  • To get a baseline tracing of the heart's function during a physical exam, which can be compared with past and future ECGs

There may be other reasons for your provider to advise an ECG.

What are the risks of an electrocardiogram?

An ECG is a quick, easy way to assess the heart’s function. Risks associated with ECG are minimal and rare.

You won't feel anything during the ECG. You may feel some discomfort when the sticky electrodes are taken off. If the electrode patches are left on too long, they may cause skin irritation.

Certain factors or conditions may interfere with or affect the results of the ECG. These include:

  • Obesity

  • Anatomical considerations, such as the size of the chest and the location of the heart within the chest

  • Movement during the test

  • Exercise or smoking before the test

  • Certain medicines

  • Electrolyte imbalances, such as too much or too little potassium, magnesium, or calcium in the blood

How do I get ready for an electrocardiogram?

  • Your healthcare provider or the technician will explain the test to you and let you ask questions.

  • Generally, fasting (not eating) isn't required before the test.

  • Tell your provider about all the prescription and over-the-counter medicines, vitamins, herbs, and supplements you take.

  • Tell your provider if you have a pacemaker.

  • Based on your medical condition, your provider may request other specific preparations.

What happens during an electrocardiogram?

An ECG may be done on an outpatient basis or as part of a hospital stay. Steps may vary depending on your condition and your healthcare provider’s practices.

Generally, an ECG follows this process:

  1. You'll be asked to remove any jewelry or other objects (cellphone) that may interfere with the test.

  2. You'll be asked to remove clothing from the waist up. You will be given a sheet or gown to wear so that only the necessary skin is exposed during the test.

  3. You'll lie flat on a table or bed for the test. It's important for you to lie still and not talk during the ECG so that you don’t change the results.

  4. If your chest, arms, or legs are very hairy, the technician may shave or clip small patches of hair so that the electrodes will stick to your skin.

  5. Electrodes will be attached to your chest, arms, and legs.

  6. The lead wires will be attached to the electrodes.

  7. Once the leads are attached, the technician may enter identifying information about you into the machine's computer.

  8. The ECG will be started. It will take only a short time for the tracing to be completed.

  9. Once the tracing is completed, the technician will disconnect the leads and remove the electrodes.

What happens after an electrocardiogram?

You should be able to go back to your normal diet and activities unless your healthcare provider tells you differently.

Generally, there is no special care needed after an ECG.

Tell your provider if you have any chest pain, shortness of breath, dizziness, fainting, or other symptoms that you had before the ECG.

Your provider may give you other instructions after the test, depending on your situation.

Next steps

Before you agree to the test or the procedure, make sure you know:

  • The name of the test or procedure

  • The reason you're having the test or procedure

  • What results to expect and what they mean

  • The risks and benefits of the test or procedure

  • What the possible side effects or complications are

  • When and where you're to have the test

  • Who will do the test or procedure and what that person’s qualifications are

  • What would happen if you didn't have the test or procedure

  • Any alternative tests or procedures to think about

  • When and how you'll get the results

  • Who to call after the test or procedure if you have questions or problems

  • How much you'll have to pay for the test or procedure

Online Medical Reviewer: Marianne Fraser MSN RN
Online Medical Reviewer: Robyn Zercher FNP
Online Medical Reviewer: Stacey Wojcik MBA BSN RN
Date Last Reviewed: 2/1/2024
© 2000-2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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