Electrocardiogram (ECG)

4-minute read

If you suspect you may be having a heart attack, dial triple zero (000) and immediately ask for an ambulance.

Key facts

An ECG is a simple, painless test that measures your heart’s electrical activity.
Your doctor may recommend an ECG if you have symptoms such as chest pain or a racing heart.
If your ECG is abnormal, you may need further tests or treatment.

What is an ECG?

An ECG is a graph of your heart's electrical activity. It’s a simple, safe and painless test. There’s no risk of being electrocuted.

Why do I need an ECG?

Your doctor may recommend an ECG if you have chest pain, a racing heart or other heart problems.

An ECG can show if you are having or have had:

a heart attack
a stressed heart muscle, due to narrowing or blockages in your heart arteries
irregular heart rhythms
pericarditis (heart lining inflammation)
abnormal heart electrical pathways

How can I prepare for an ECG?

You don’t need to do anything special to prepare for an ECG. Before the ECG, you may have your chest, arm or leg hair shaved or skin cleaned so the electrodes stick on your body properly. If you are wearing a bra, you might be asked to take it off.

Who performs ECGs?

A nurse, ECG technician or a doctor will perform your ECG.

What happens during the ECG?

During an ECG, leads are attached to electrodes using sticky dots that are placed on your arms, legs and chest. The leads connect to a machine, which takes the reading.

illustration of a gastric bypass — The ECG electrodes must be placed on clean, dry, skin. Sometimes, you will need to have the area shaved to ensure good skin contact.

What are the different types of ECG?

Different types of ECG include:

Resting ECG: you lie still for a few minutes and breathe normally while the ECG is recorded.
Ambulatory ECG (also called a 24-hour ECG, or Holter monitor): you wear the leads and carry a monitor while you go about your usual activities for 24 hours.
A cardiac stress test: the ECG is recorded while you exercise on a treadmill. It checks for areas of heart muscle that struggle when stressed. If you cannot exercise, medicines might be used to test the effect of stress on your heart.

If you have chest pain or another problem during the ECG, it’s important to tell the technician doing the test.

If you're having an ambulatory ECG, the technician may give you a diary to record of any symptoms.

What happens after my ECG?

A trained doctor or nurse will look at the ECG pattern and interpret what it says about your heart. Your doctor will discuss the results with you. If your doctor notices a serious problem in your ECG, you may need to begin treatment. Sometimes you may need other tests, like an ultrasound of your heart (echocardiogram), blood tests or an angiogram (pictures of the heart's blood vessels).

Should I use a smartphone or smartwatch ECG application?

Some heart problems are challenging to diagnose if your symptoms don’t occur while you’re having the ECG. Some smartphone and smartwatches can reconstruct an ECG from your pulse waveform. This could be useful in diagnosing heart rhythm abnormalities, but the accuracy of these applications and devices isn’t known. There are studies that are checking this.

If you wear a smartphone or smartwatch regularly, you can mention this to your doctor, who may find the tracking information useful.