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Electrocardiogram (ECG)

An electrocardiogram (ECG) is a test that can record the rhythm and electrical activity of your heart to find out if it’s healthy.

Your GP might give you an ECG if you have symptoms of a heart condition. Sometimes an ECG is one of the tests you have before an operation. If you’re taken to hospital with chest pain or an abnormal heart rate, you may have an ECG too.

An ECG measures the electrical signals that cause your heart to beat. During the test, a number of wires are connected to your arms, legs and chest and these pick up the electrical signals. They can be sent to a monitor or traced out on a piece of paper. An ECG can show different heart problems including:

  • if you’re having a heart attack, or your heart has been damaged by a previous heart attack
  • an enlarged heart that’s under strain
  • fast, slow or irregular heartbeats called arrhythmias
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How the heart works
Your heart is designed to last a whole lifetime


  • Types Types of ECG

    There are a number of different types of ECG, some of which we’ve explained below.

    • A standard ECG. This is sometimes called a resting ECG and will be taken while you’re lying down.
    • An exercise ECG (stress test or treadmill test). This is done while you’re exercising – such as walking on a treadmill – to show how your heart copes under stress. The test can help to find out if you have coronary heart disease, which is when the arteries to your heart become narrowed. If you’ve recently had heart surgery or a heart attack, it can help your doctor to work out how much exercise is safe for you.
    • A 24-hour ECG. In this type of ECG, you wear an electronic recorder for a day or two. It’s sometimes called a Holter monitor or ambulatory ECG. It records the activity of your heart over a day and night and can help to show irregular heartbeats that may only happen occasionally.
    • Cardiac event recorders. These can record your heartbeat over a longer period of time. There are two main types of recorders. Portable event recorders are devices which you hold up to your chest and turn on when you’re having symptoms. Implantable loop recorders (ILR) are devices placed under the skin on your chest. These continuously monitor your heartbeat for up to two years. They can record symptoms that don’t happen very often, such as dizzy spells or fainting.
  • Preparation Preparing for an ECG

    You can have a resting ECG at your GP practice and you don’t normally need to prepare for this.

    With other types of ECG, you’ll need to go to hospital to have the test, or to have the equipment fitted. You can go home the same day and won’t need to stay overnight in hospital.

    If you’re having an exercise ECG, it’s best to wear comfortable clothes and shoes. Don’t eat a big meal just before the test in the same way you probably wouldn’t before doing any exercise. Your hospital may ask you to stop taking some of your medicines a day or two before your exercise ECG. Your doctor will let you know in advance if you need to do this.

    Your doctor, nurse or technician will discuss with you what will happen before, during and after your procedure. This is a chance for you to understand exactly what will happen. You might find it helpful to think about any questions you want to ask. This will help you to feel fully informed about the procedure so you can give your consent for it to go ahead.

    Bupa On Demand: ECG test

    Want to talk to a Bupa consultant about having an ECG test? We’ll aim to get you seen the next day. Prices from £250.

  • The procedure What happens during an ECG?

    Resting ECG

    It only takes about five minutes to have a standard, resting ECG. Your nurse, technician or doctor will ask you to take off your clothing above your waist and lie on a bed or couch. They will stick some patches called electrodes onto your arms, legs and chest. If you have a hairy chest, they might need to shave some small patches to help the electrodes stick to your skin. Once you have the electrodes on, your doctor, nurse or technician can cover you with a gown if you wish.

    Whoever is doing your ECG will then attach the electrodes with wires to a recording machine. When your heart beats, it produces electrical signals and these are picked up by the electrodes and transmitted to the recording machine. The machine will print a record of your heartbeat onto a paper strip or store the data on a computer. Try to lie still and relax as much as possible during the recording – moving or tensing your muscles can affect the recording.

    Exercise ECG

    An exercise ECG usually takes about 20 minutes. Electrodes will be attached to you from the recording machine in the same way as in a standard ECG. You’ll then be asked to start walking on a treadmill or cycle on an exercise bike at a gentle, slow pace. As the test goes on, the slope or speed of the treadmill will increase or the bike will become harder to pedal. This will make your heart work harder.

    Your ECG will be monitored every few minutes while you’re exercising, along with your blood pressure and heart rate. The test will finish when whoever is doing your test has the readings they need. This is often when you reach a level of exercise that’s been decided in advance. They may also stop the test if your blood pressure changes, you have chest pains or become short of breath. You can also ask for the test to be stopped at any time if you feel unwell.

    24-hour ECG

    For this test, you’ll wear a small, portable recorder that’s attached to a belt you wear around your waist. You’ll have up to six small patches (electrodes) stuck onto your chest and these connect to the recorder with wires.

    You can go about your normal activities while you’re wearing the 24-hour recorder but don’t have a bath or shower with the recorder on. You may be asked to keep a diary of everything that you do during the test and note down if you have any symptoms. After the 24 hours are up, you’ll need to go back to hospital to return the recorder and find out what the results showed. You might need to wear it for longer if your doctor thinks it would be useful to track your heart’s activity over more time.

    Cardiac event recorders

    A portable cardiac event recorder is a small electrical device that you carry with you all the time. When you have symptoms, such as palpitations, you put it on your chest and switch it on to record your ECG. You’ll be given instructions on what you need to do to send the readings to your hospital so they can be analysed. Someone will get in touch with you to tell you what to do next.

    An implantable loop recorder (ILR) is a small, slim device that your doctor will place just under the skin on the front of your chest. You’ll have a local anaesthetic so you’ll stay awake but won’t feel any pain while this is being done.

    An ILR will continuously monitor your heart and record any unusual heartbeats. You can also start a recording if you notice any symptoms.

  • Aftercare What to expect afterwards

    Your doctor will look at the ECG recording to get an idea of whether you have a heart condition. Depending on where you have your test and who does it, you may get the results straight away or at your next appointment.

    Heart problems don’t always show up on an ECG. On the other hand, your ECG may look abnormal even if your heart is healthy. You may need to have more tests, such as an echocardiogram, to find out more if your doctor thinks there’s a problem. Or, if your heart looks normal, to look into what’s causing symptoms.

  • ECG tests on demand

    You can access a range of our health and wellbeing services on a pay-as-you-go basis, including ECG tests.

  • Risks What are the risks?

    A standard ECG is a very simple procedure and is completely painless. The recording machine can’t give you an electric shock or affect your heart in any way.

    There is a very small risk of complications during an exercise ECG. The extra strain on your heart from exercising may cause:

    You’ll be monitored at all times during the test. If your doctor, nurse or technician thinks there is any risk of you becoming unwell, they will stop the test.

  • FAQ: What does an ECG show my doctor? FAQ: What does an ECG show my doctor?


    The print-out produced after your electrocardiogram (ECG) will show your doctor the rhythm and rate of your heart. It may also show signs of any problems, such as if you’ve had a heart attack before.

    More information

    An ECG recording looks like a wavy line, with a series of bumps and spikes. These are waveforms that relate to the different phases of each heartbeat. Your doctor will look at each part of your ECG recording. They can see if there are problems with any areas of your heart or with the way it’s beating.

    In a normal heartbeat, the waveform is the same in each heart beat, and similar in everyone. If you have a problem with your heart, the waveforms may look different. They may be too big or too small, too close together or too far apart, or some of the bumps may be missing. How the waveforms look depends on what’s wrong with your heart.

    Your doctor will look at the ECG recording to get an idea of whether you have a heart condition. However, heart problems don’t always show up on an ECG, or your ECG may look abnormal even if your heart is healthy. If your doctor thinks there’s a problem, you may need to have more heart tests, such as an echocardiogram.

  • FAQ: What problems can cause an abnormal ECG? FAQ: What problems can cause an abnormal ECG?


    An ECG can show a number of heart conditions. But bear in mind too that an abnormal ECG doesn’t always mean that there’s something wrong with your heart.

    More information

    An ECG can help your doctor find out about any heart problems, how severe these are and what kind of treatment you may need.

    An abnormal ECG can be caused by various heart conditions, as well as other things including:

    Some medicines, including beta-blockers and digoxin, can also cause an abnormal ECG.

  • FAQ: What happens if I can't finish the exercise ECG? FAQ: What happens if I can't finish the exercise ECG?


    If you feel really tired, dizzy or unwell, you can ask to stop the test. But you’ll be encouraged to do as much as you can so you get the most value from the test.

    More information

    An exercise ECG is designed to see how well your heart works when you’re being active and putting a bit more strain on your heart. As the exercise gradually increases during the test it may make you feel uncomfortable and you may feel a little out of breath. The test isn’t an intensive workout and it’s quite likely that you’ll find you can do more than you expect and complete the test fine.

    You’ll be monitored all the time while you have the test. The nurse, technician or doctor doing the test will check your blood pressure, heart rate and ECG throughout. They will ask you to stop if they record a sudden change in your blood pressure or heart rate. They will also stop the test if you have any symptoms, such as chest pain, trouble breathing or if you feel dizzy. And you can ask to stop the test at any time if you start to feel unwell.

    If you can’t do the test because of a health condition like severe arthritis, your doctor may arrange for you to have other tests instead. If you can walk easily, you’re fit enough to do the test.

  • Resources Resources

    Further information


    • Clinical guidelines by consensus: recording a standard 12-lead electrocardiogram. Society for Cardiological Science and Technology., published June 2014
    • Tests. British Heart Foundation., published 31 October 2014
    • Cardiac tests. Medscape., published 18 December 2014
    • ECG a methodical approach. PatientPlus., reviewed 25 January 2013
    • Assessment of palpitations. BMJ Best Practice., published 22 September 2014
    • Treadmill stress testing. Medscape., published 18 March 2014
    • Exercise tolerance testing. PatientPlus., reviewed 14 March 2012
    • Electrocardiography (ECG). The Merck Manuals., published October 2013
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