Electrocardiogram

An electrocardiogram (an ECG or EKG) is a simple test that looks at your heart rate, rhythm and electrical activity. Your heart’s electrical activity is what coordinates your heartbeats. Heart conditions can interfere with this electrical activity. 

During an ECG, sensors are attached to your skin to record your heart’s electrical activity. This can help your doctor diagnose or monitor a wide range of heart conditions including: 

• Arrhythmia — an irregular heartbeat eg too fast, too slow or missed beats
• Cardiomyopathy — where the walls of your heart have thickened
• Coronary heart disease or angina — where the blood supply to your heart is reduced by a build-up of fatty substances in the blood vessels supplying your heart
• Heart attack — where the blood supply to your heart is suddenly stopped
• Structural abnormalities of your heart — eg enlarged heart chambers, an enlarged heart wall and heart defects 

It can also be useful to rule problems out and it’s usually one of the first heart tests you’ll have if your doctor suspects something is wrong.

An electrocardiogram (ECG) is not to be confused with an echocardiogram, which is a scan of your heart’s structures. 

If your doctor or a doctor specialising in treating heart conditions (a cardiologist) thinks you may have a problem with your heart, they may recommend that you have an ECG to help work out the cause of symptoms such as:

• An irregular heartbeat or unusual sounds detected when listening to your heart with a stethoscope 
• Chest pain
• Dizziness and/or fatigue
• Heart palpitations
• High blood pressure
• Shortness of breath

If you have already been diagnosed with a heart condition or are taking medication that could affect the health of your heart, you may have a series of ECGs over time to monitor your heart’s condition. This may also be done to check that treatment for a heart condition (eg a pacemaker) is working correctly.

A referral letter from a consultant or GP is required before booking any diagnostic investigation.

Before your electrocardiogram

You will need a referral letter from a consultant or GP before booking any diagnostic investigation, including an electrocardiogram.

You don't need to prepare for your electrocardiogram in any special way and can eat and drink as usual. At your appointment, you may need to remove your upper body clothing so that the ECG sensors can be attached to your wrists and chest, as well as your ankles. You may also need to have your chest area shaved or cleaned. 

During your electrocardiogram 

Once the sensors are placed on your chest, you may be given a hospital gown to wear. The sensors will record electrical signals produced by your heart each time it beats to look at your heart’s rate, rhythm and electrical activity. 

For standard ECGs, you'll need to breathe normally and lie still. It's is therefore important to make sure you feel comfortable and warm, as moving or shivering could affect your ECG results. 

Once your electrocardiogram is complete, you can return to your normal activities.

Types of electrocardiograms

There are different types of ECG tests. Your doctor will recommend the most suitable one based on the suspected heart problem and your symptoms. You may therefore have: 

• Standard ECG: This is taken while resting in a clinic or hospital. The sensors on your skin are connected to an ECG machine, which shows your recordings to a doctor.
• Stress ECG: This is similar to a standard ECG, except the recordings are taken while you’re physically exerting yourself (eg on a treadmill or exercise bike) to see how well your heart works when you’re more active. It may be recommended if your symptoms tend to occur during physical activity.
• ECG monitoring: This is also called Holter monitoring or an ambulatory ECG, which allows for your heart’s activity to be recorded over 24 to 48 hours. In a clinic or hospital, three sensors will be placed on your chest and the attached wires taped down. The wires  connect to a small portable device attached to a belt worn around your waist. You can then return home and continue with your normal activities. However, you can’t have a bath or shower during your ECG monitoring. The procedure is safe and painless. Once complete, you'll return the device to the hospital and your results will be analysed. It may be recommended if your symptoms are unpredictable, random and short-lived. It can help diagnose atrial fibrillation or skipped heartbeats that don’t happen often.

This depends on the type of ECG you have. A standard ECG takes a few minutes, whereas ECG monitoring may be taken over one or two days while you’re at home. A stress ECG usually lasts for up to 12 minutes.

The ECG will be carried out by a specially trained healthcare professional, which may be your consultant, a nurse or your GP. They may be able to discuss your results straight away or they’ll pass on a report to the doctor who requested the test. We try to get your results back to you as soon as possible as less waiting means less worrying.

Depending on your ECG results, you may need further tests to help identify the cause of any problems you’re having. 

An ECG is a quick and safe test. No electricity will be passed into your body. You may feel some discomfort when the sticky sensors are removed and some people experience a mild rash where they were attached. 

During stress ECGs, you'll be carefully monitored, so if you experience any symptoms or feel unwell, the ECG will be stopped.