Electrocardiogram (ECG)

Your health expert: Professor Mark Westwood, Consultant Cardiologist
Content editor review by Rachael Mayfield-Blake, Freelance Health Editor, November 2022.
Next review due November 2025.

An electrocardiogram (ECG) is a test to record the rhythm and electrical activity of your heart. It can help to find out if there are any problems with your heart.

About ECG

A doctor may advise you to have an ECG test if you have symptoms of a heart condition. These might include chest pain, palpitations (when you can feel your heart thumping or throbbing), shortness of breath and dizziness.

You may need an ECG test to check your heart if you have other health conditions too, or if you’ve had an accident or injury. It can also be one of the general health tests you have before an operation.

In an ECG test, a health professional will attach sensors with sticky pads to your chest, arms and legs. The sensors pick up electrical signals from your heart. These are sent to an ECG machine, which records the signals and prints out a reading on paper.

An ECG can detect 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
  • heart valve disease

Ask your doctor why you need to have an ECG test, and what it may show.

Types of ECG

The type of ECG test you have will depend on your symptoms and what type of heart problem you might have. There are three main types of ECG.

  • A resting or standard ECG – this is done while you lie down and relax. It usually only takes a few minutes to do.
  • An exercise ECG – this is done while you exercise, usually when you walk on a treadmill or cycle on an exercise bike. It shows how your heart copes under strain. You may have this test to investigate irregular heartbeats that happen when you exercise, or to help find out if you have coronary heart disease, although it’s used less often for this now.
  • An ambulatory (24-hour) ECG or Holter monitor – for this test, you wear an electronic recorder for up to two weeks. It records the activity of your heart over this time and helps to show irregular heartbeats that may only happen occasionally.
  • A monitoring patch – you stick the patch onto your chest (there aren’t any wires) and it records the electrical activity of your heart. You can use it for up to two weeks.

If you get abnormal rhythms (palpitations) from time to time but not every day, your doctor may recommend a device called a cardiac event recorder. This can record your heartbeat over a longer period of time. There are two main types.

  • Portable event recorders are devices that you carry or wear and activate yourself when you have symptoms.
  • Implantable loop recorders (ILR) – these are recording devices that are placed under the skin on your chest.

If your doctor recommends a particular type of ECG, they’ll give you information about the test and what it involves.

Preparation for an ECG

You don’t normally need to prepare in any way for a resting ECG. You may be able to have this test at your GP practice. It’s best not to use any oils or moisturisers on your skin when you go for the ECG because the sticky pads may not stick. It’s also a good idea not to wear too many layers or anything that’s difficult to remove because you’ll have to undress (from your waist up) to have the ECG.

You usually go to hospital to have an exercise ECG, an ambulatory ECG, or an event recorder. Your hospital will give you any information you need about how to prepare.

For an exercise ECG, it’s best to wear comfortable clothes and shoes. Your hospital may ask you not to eat a heavy meal or have any caffeinated drinks for a few hours before the test. They may also ask you to stop taking some of your medicines a day or two before your exercise ECG. But only stop your medicines if they tell you to.

ECG procedure

The health professional (practitioner) who will do your ECG test will talk to you beforehand to explain exactly what will happen and what you can expect. Ask any questions you have. It’s important that you understand what will happen before you give your consent to go ahead.

Here we give some general information about what may happen during these tests. Your experience may be different in some ways. Always follow the instructions your doctor or hospital gives you.

Resting ECG

It only takes a few minutes to have a resting ECG and you won’t feel any pain.

Your ECG practitioner will ask you to take the clothes off your top half (anything above your waist) and lie on an examination bed. They’ll prepare the areas of your skin where they will stick the electrodes. They may need to clean your skin, exfoliate it with a paper towel or shave any hair with a razor. Your practitioner will check with you before they do this. They’ll then put the electrodes in position on your arms, legs and chest, using sticky patches. Once you have the electrodes on, your practitioner will cover you with a gown.

The electrodes are connected by wires to a recording machine. When you’re ready, your ECG practitioner will begin a recording on the 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 – if you move or tense your muscles, it can affect the recording. Once your practitioner has got a good recording, they’ll remove the electrodes from your body.

Exercise ECG

An exercise ECG usually takes about 15 minutes. Your health professional will attach electrodes to your shoulders and chest and connect these to an ECG recorder. They’ll then ask you to start walking on a treadmill or cycle on an exercise bike at a gentle, slow pace. As the test goes on, the slope and speed of the treadmill will increase or the bike will become harder to pedal. This will make your heart work harder.

The ECG practitioner will monitor your ECG while you’re exercising, along with your blood pressure. They won’t make you do more than you’re able to manage. But if you have any chest pains, shortness of breath or feel unwell in any way, let them know and they can stop the test. For more information about not being able to complete the exercise, see our FAQ below: what happens if I can’t finish the exercise ECG?

24-hour ECG

In a 24-hour ECG, a health professional will stick three electrodes to your chest and connect these to a small, portable recorder. You wear this on a belt around your waist.

You can go about your normal activities while you wear the 24-hour recorder but don’t have a bath or shower with the recorder on. Your hospital may ask you to keep a diary of everything that you do during the time period 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. 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.

Monitoring patch

An alternative to an ambulatory (24-hour) ECG, or Holter monitor, is a monitoring patch. This is a sticky patch that you put on the top left side of your chest. You can either go to hospital to have it put on, or you can fit it yourself at home. The patch continuously records the electrical activity of your heart, but you can also press a button if you feel symptoms. It’s a good idea to keep a diary to note down any symptoms you have too.

You wear it for a set time (your doctor will tell you for how long) and you then remove the patch and post it to a company to analyse your results. Your doctor will then receive a report and go through this with you.

Cardiac event recorders

A portable cardiac event recorder is a small electrical device that you wear or have on you all the time for up to a month (usually about a week or two). You’ll usually either hold it, or wear it on your wrist – you don’t wear electrodes on your chest for these monitors. When you have symptoms such as chest pain, dizziness or palpitations, you press a button and the device will record your ECG. Sometimes, you’ll need to place the device on your chest, but your doctor will explain exactly how your event recorder works. They’ll also show you how to send your ECG recordings to the hospital using your phone.

An implantable loop recorder (ILR) is a small device that your doctor will place just under the skin on the front of your chest, near your shoulder. You’ll have a local anaesthetic when they fit the ILR (you’ll stay awake but won’t feel any pain). An ILR will continuously monitor your heart and record any unusual heartbeats. You can also start a recording if you notice any symptoms. Your ILR will stay in place until your doctor is able to diagnose any problems (this can be up to three years). They’ll then remove it in a procedure similar to when it was put in.

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Aftercare following ECG

Your doctor will use your ECG test results, alongside other tests, to help assess if you have a heart condition. Sometimes, your doctor may discuss the results of the ECG with you straight away, but sometimes it needs to be sent to a specialist to check. The results will then be sent to the doctor who ordered your test.

An ECG can give doctors an idea if there are problems with your heart, but it doesn’t always give all the information they need. Heart problems don’t always show up on an ECG. If your resting ECG looks normal, you may need more tests – including other types of ECG – to look into what’s causing your symptoms.

Sometimes your ECG may look abnormal even if your heart is healthy. You may need to have other tests, such as an echocardiogram, to find out more.

Side-effects of ECG

A resting ECG is a very simple procedure and is completely painless. The recording machine doesn’t send any electricity into your body – it just records your body’s own electrical activity.

When the electrode stickers are removed, this might feel a little bit uncomfortable – a bit like having a sticking plaster removed. It’s possible you might have some redness and swelling on your skin afterwards because of a reaction to the adhesive used, but this is rare.

Complications of ECG

There’s a very small risk that the extra strain on your heart during an exercise ECG test may trigger problems with your heart. This is very unlikely though, as you’ll be monitored at all times during the test. If your doctor, nurse or technician thinks there’s any risk of you becoming unwell, they’ll stop the test.

An ECG records the electrical activity that spreads through your heart as it beats. The recording looks like a wavy line, with a series of bumps and spikes, which relate to the different phases of your heartbeat. A normal ECG follows a similar pattern in everybody. If you have a problem with your heart, the waves may look bigger or smaller, too close together or too far apart. Or, some of the bumps may be missing. How the waves look depends on what’s wrong with your heart.

See the section about ECG above for more information.

An ECG can show if you have a heart condition, such as a heart attack or coronary heart disease. But an abnormal ECG doesn’t always mean that there’s something wrong with your heart. Sometimes medicines, such as antidepressants, can affect an ECG. Other things that can have an effect are if you’re anxious or if you’ve had a hot or cold drink. Your doctor will take all these things into account when they analyse your results.

See the section about ECG above for more information.

An exercise ECG is designed to see how well your heart functions when it’s working a little harder. As the exercise gradually increases during the test, it may make you feel uncomfortable and you may feel a little out of breath. But it shouldn’t be more than you can manage. If you feel really tired or unwell, you can ask to stop. But try to do as much as you can so you get the most value from the test. If you’re unable to finish, your doctor may refer you for other tests, such as scans of your heart.

See the section on the ECG procedure for more information.

An ECG can test for a range of heart problems from heart attacks to fast, slow or irregular heartbeats called arrhythmias, for example. An ECG test can also check your heart if you’ve had an accident or injury. It can also be one of the general health tests you have before an operation to check you’re well enough to have it.

See the section about ECG above for more information.

You don’t normally need any special preparation for a resting ECG.

If you’re having an exercise ECG, wear comfortable clothes and shoes since you’ll be exercising in these. It’s usually best not to eat a heavy meal or have any caffeinated drinks for a few hours before the test. Your hospital may ask you to stop taking some of your medicines a day or two before your exercise ECG. But only stop your medicines if they tell you to.

See the section on preparation for an ECG above for more information.

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