Electrocardiogram (ECG)

ECG explained

What is an ECG?

An electrocardiogram, or ECG, is a simple and useful test which records the rhythm, rate and electrical activity of your heart.

An ECG can help detect problems with your heart rate or heart rhythm. It can help doctors tell if you’re having a heart attack or if you’ve had a heart attack in the past.

An ECG is usually one of the first heart tests you'll have. It does have some limitations, so often you will have one or more other tests too. An abnormal ECG reading does not always mean there's something wrong with your heart.

During an ECG

What happens during an ECG?

Ten small sticky patches called electrodes are put on your arms, legs and chest. These are connected by wires to an ECG machine which picks up the electrical signals that make your heart beat. This electrical activity is recorded and printed onto paper. Below is what a normal ECG would like.

How long will an ECG take?

The whole test takes a few minutes and is completely painless. You will need to lie still as moving can affect the results.

Types of ECG

What is an exercise ECG?

This is an ECG that is recorded while you're walking on a treadmill or cycling on an exercise bike. The aim of this test is to see how your heart works when you're more active.

Find out more about what an exercise ECG involves.

What is a 24-hour ECG recording?

Also called Holter monitoring or ambulatory ECG monitoring, this involves continuously recording your heart’s electrical activity for 24 to 48 hours, sometimes longer. This can help diagnose conditions such as atrial fibrillation or uncover the cause of palpitations, which do not happen all the time.

During a 24-hour ECG recording:

You’ll have electrodes put on your chest and the wires attached to these will be taped down.
You’ll wear a small portable recorder on a belt around your waist which the wires will lead to.
While you’re wearing the ECG recorder, you can do everything you would normally do except have a bath or shower.
It's safe and completely painless but some electrodes can be very sticky, so let the team know if you have sensitive skin.
When the test is finished, you’ll return the recorder to the hospital so the results can be analysed.

What is a cardiac event recorder?

If you have symptoms that do not happen frequently, your doctor might suggest having a cardiac event recorder or an implantable loop recorder (also known as ILR) inserted. This records the heart's activity for a longer period of time, or whenever symptoms occur.

An ILR is implanted under the skin on your chest in a minor surgical procedure done under local anaesthetic. An ILR can continuously monitor your heartbeat for up to three years and help find out what may be causing your symptoms, such as dizzy spells or blackouts.

This is particularly useful for people who have symptoms that have not been picked up through a standard ECG or Holter monitor.