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Electrocardiogram (ECG)

  • About ECGs
  • Preparing for your test
  • About the test
  • Getting your results
  • What are the risks?
  • Further information
  • Sources
  • Related topics

About ECGs

An ECG is a simple test to record information about your heart beat. It involves using wires connected to your arms, legs and chest to pick up the electrical signals produced by your heart. These signals can be seen on a screen or are traced out on a piece of paper.

There are a number of reasons why you may need to have an ECG. You may have one:

  • to check for problems with your heart, if you are having symptoms such as palpitations, dizziness or chest pain
  • to check how well your heart is functioning, before an operation
  • as part of a routine health check-up

The test can detect various problems with your heart, including an abnormal heartbeat or if the heart is working under strain. It may also show if you have had a heart attack.

Types of ECG

  • The standard ECG is sometimes called a resting ECG, as it is taken while you are not doing any activity.
  • An exercise ECG (also known as a stress test or treadmill test) is taken while you carry out some form of controlled exercise, in order to see how your heart copes under stress. The test can help to diagnose coronary heart disease (when the arteries to the heart become narrowed) and assess how severe it is.
  • A 24-hour ECG, sometimes called a Holter monitor or ambulatory ECG, involves wearing an electronic recorder for 24 hours. Your doctor can then assess the activity of your heart over the course of a day, and particularly at any times when you have symptoms. This test is useful in detecting whether you have an irregular heartbeat (arrhythmia).
  • Cardiac event recorders are devices that can record your heart's activity over a longer period of time. They include portable event recorders, which you just use whenever you get symptoms, and implantable loop recorders (ILR), which are implanted under the skin in your chest to continuously monitor your heartbeat.

Preparing for your test

A standard ECG can often be done at your GP practice. No preparation is normally needed for this. Sometimes (particularly if you are having an exercise ECG) you will need to have the test in a hospital.

You will be asked to attend hospital as an out-patient and should follow any instructions given to you in your appointment letter. For an exercise ECG, you will probably be advised not to eat a heavy meal before the test and will be advised what clothing to wear. If you are taking certain medicines, you may also be told to stop these before having an exercise ECG.

At the hospital, your doctor will discuss the test with you and ask you to sign a consent form. This confirms that you have given your permission for the test to go ahead.

About the test

Resting ECG

The standard, resting ECG, is very simple and only takes a few minutes - you will be able to sit or lie down while having it. You may be asked to undress to the waist before the test begins. You will have a number of sticky patches called electrodes stuck or strapped to you (one on each arm and leg and six on your chest). If you have a very hairy chest, some small patches may need to be shaved to allow the electrodes to make contact.

The electrodes are attached to a recording machine by wires. When your heart beats, it produces electrical signals which are picked up by the electrodes and transmitted to the recording machine. The machine then prints out your heartbeat onto a paper strip.

Exercise ECG

If you have an exercise ECG, electrodes from the recording machine will be connected to you with wires in the same way as a standard ECG. Your heart rate and blood pressure will also be recorded. You will then be asked to exercise - either by walking on a treadmill or cycling on a stationary exercise bike.

The exercise will be very easy to start with, and then is gradually made harder (for example, by increasing the speed or the slope of the treadmill). The doctor or technician will continue to monitor your ECG along with your blood pressure and heart rate, every few minutes while you are exercising.

The test will last between a few minutes and 15 minutes. It will be stopped when you have reached your target heart rate, or if you ask for it to be stopped earlier. Once your ECG and blood pressure have returned to normal, you will be able to go home.

24-hour ECG

In this test, you will be asked to wear a small portable recorder, which you can wear on a belt around your waist. Wires from the recorder will be attached to you with three or four small sticky patches (electrodes) on your chest.

You will be sent home and asked to carry out your normal activities for the day, keeping a diary of everything that you do and noting any times when you feel symptoms. At the end of the 24 hours, you will return to the hospital to have the monitor taken off and the results analysed. This type of test can also sometimes be carried out over a longer period - up to a week, rather than just 24 hours.

Cardiac event recorders

If you are having a portable event recorder, you will be given a small electrical device that you keep with you to use whenever you get symptoms. When you have symptoms, you will need to place the device on your chest and switch it on to record your ECG. With most portable event recorders, you will be able to send the results of your ECG recording to the hospital by holding the device to a phone. You will be shown how to do this. The doctor or technicians at the hospital can then analyse your results.

If you are having an implantable loop recorder (ILR), you will need a very simple procedure to have the device fitted. An ILR is a small, slim device that is inserted just under the skin in the front of your chest. You will have a local anaesthetic, so you won't feel any pain. The device will continuously monitor your heartbeat. It can record any abnormal heartbeat that it's programmed to detect, and can also be set to record times when you experience any symptoms. Your doctor can then examine the information on your heartbeat at that time.

Getting your results

If your GP carries out your ECG, he or she may discuss the results with you immediately after the test. If you have the test in hospital, your results will be sent to the doctor who requested your test, who will discuss them with you at your next appointment.

What are the risks?

An ECG is a very simple procedure and is completely painless. There is no way that the recording machine can give you an electric shock or affect your heart in any way.

There is a very small risk of complications with the exercise ECG. The extra demand on your heart from exercising can occasionally cause your heart to beat abnormally (an arrhythmia) or a heart attack. However, you will be constantly monitored and told to stop if the technician or doctor thinks there is a risk of this happening. A medical team will always be on hand in case of emergency.

Further information

British Cardiac Patients Association

British Heart Foundation


  • Tests for heart conditions. British Heart Foundation, May 2004, Health information series number 9. www.bhf.org.uk
  • Electrocardiograph - ECG. British Cardiac Patients Association, 2007. www.bcpa.co.uk
  • Simon C, Everitt H, Kendrick T. Oxford Handbook of General Practice. 2nd ed. Oxford: Oxford University Press, 2005:310-313
  • Protocol for cardiac physiologist managed exercise stress testing. British Cardiac Society, 2003. www.bcs.com

Related topics

Diagnosing heart conditions