ECG (electrocardiogram)

An ECG is a test to check the electrical activity of your heart. It can show changes to your heart rate or rhythm and tell your doctor how well your heart is working.

ECG stands for electrocardiogram. You might also hear this test called a heart trace. An ECG can give your doctor a lot of good information. It can help the doctor decide if you need further tests.

To have the test a trained health care professional puts small sticky pads on your chest, arms and legs. Wires connect these to an ECG recording machine; these wires are ECG leads. There are usually 10 small sticky pads and wires in total. The different wires look at the heart from different places - similar to taking pictures of your car from the front, top, sides and back.

The ECG machine shows your heartbeat as an electrical trace on a screen. Your doctor can see the heartbeat and rhythm on a TV screen or print it out on paper.  

Below is a picture of an ECG printed on paper.

Diagram showing an ECG printed on paper

You might have an ECG in a clinic, on a ward or in a GP surgery. It takes about 5 minutes. A trained healthcare assistant, nurse or doctor does the ECG for you.

Some people need to have an ECG machine on for monitoring for a day or so. This means they have a portable machine that they can carry around. This is an ambulatory ECG machine. This test has less ECG sticky pads and leads.

An ECG doesn’t hurt and you can’t feel anything when you have this test. 

Why do I need an ECG?

You might have an ECG:

  • before and during some cancer treatments that may affect your heart. This is so your doctor can check for any changes
  • if you become unwell during cancer treatment
  • before or during an operation or test that may affect the heart
  • if you have a heart condition that needs monitoring
  • if you are taking part in a clinical trial

How do you have an ECG?


There is no special preparation before an ECG. You usually remove or loosen some of your clothes on the top half of your body.

You may need to remove your shoes, socks or bra. You lie on a couch, flat or slightly upright. If you have a lot of chest hair this may be shaved. These preparations allow the sticky pads to make good contact with the skin. The pads need to be in certain positions. It may take a few minutes to get the pads and ECG leads in the right places.

During the ECG

The person doing the ECG will explain what will happen. You have the test in private, either in a separate room or behind curtains.

The person doing the tests places the sticky pads across your chest, with one pad on each wrist and ankle. They connect the ECG leads to the sticky pads.

Photo showing a women having an ECG

When the ECG machine is ready, they press a button to get a trace of your heart. You won’t feel anything. You should relax and lie still to make sure the test is accurate. You don’t need to hold your breath.

Photo showing a nurse doing an ECG

After the test

After the test the leads from the pads are unclipped. You can then remove the sticky pads.

You can get dressed and return home or to work.

Getting your results

You might get your results the same day or within 1 to 2 weeks. This depends on how quickly your doctor needs the results.

Ask your doctor or nurse how long it will take to get them. 

Are there any risks having an ECG?

An ECG is a safe, quick and painless test. 

You might have some discomfort when you remove the sticky pads.

More information

We have more information on tests, treatment and support if you have been diagnosed with cancer.

  • The Royal Marsden Manual of Clinical Nursing Procedures (9th edition)
    L Dougherty and S Lister
    Wiley Blackwell, 2015

  • Oxford handbook of clinical medicine (10th edition)
    M Longmore and others
    Oxford University Press, 2017

  • Basic Electrocardiography
    B G Petty
    Springer, 2016

  • Clinical Guidelines by Consensus: Recording a Standard 12-Lead Electrocardiogram. An Approved Method by the Society for Cardiological Science and Technology (SCST). 
    B Campbell and others
    Society for Cardiological Science and Technology, 2017

Last reviewed: 
28 Jan 2022
Next review due: 
28 Jan 2025

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