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External cardioversion

4-minute read

What is an external cardioversion?

An external cardioversion is a procedure to treat an abnormal heart rhythm. It involves connecting you to a defibrillator machine that gives a controlled electric shock to make your heart beat normally again.

Your heart is a muscle that pumps oxygen-rich blood from your lungs around your body and oxygen-poor blood from your body to your lungs. The pumping (heartbeat) is controlled by electric impulses from a group of cells on your heart called the sinus node.

When your heart beats normally, the electric impulses cause the upper collecting chambers (atria) and lower pumping chambers (ventricles) to contract and relax in a co-ordinated way.

An external cardioversion is usually recommended to treat atrial fibrillation, where the atria contract too fast and in an unco-ordinated way.

Atrial fibrillation prevents your heart from pumping as effectively. This can cause you to get palpitations (your heart beating fast or irregularly), and to feel breathless and tired. It can also sometimes cause you to have chest pain, dizziness, or to collapse.

What are the benefits of an external cardioversion?

Your heart should start to beat normally again.

Are there any alternatives to an external cardioversion?

Medication can be used to treat some symptoms of atrial fibrillation and reduce the risk of having a stroke but medication may not be as effective as an external cardioversion in relieving your symptoms.

If your atrial fibrillation is caused by abnormal electric activity from your pulmonary veins (the blood vessels that bring oxygen-rich blood from your lungs to your heart), you may be able to have a catheter ablation.

What does the procedure involve?

External cardioversion usually takes 10 minutes.

External cardioversion is usually performed under a general anaesthetic.

The healthcare team will place sticky pads on your chest or arms so they can monitor your heart during the procedure. They will also place large sticky pads on your front and back, which will be connected to a defibrillator machine.

Your heart specialist will use the machine to give you a controlled shock to make your heart beat normally again.

What complications can happen?

Some complications can be serious and can even cause death.

  • inability to restore a normal heart rhythm
  • soreness, where the large sticky pads are placed on your chest
  • change in your heart rhythm
  • low blood pressure
  • fluid collecting on your lungs
  • allergic reaction
  • stroke
  • recurrence of an abnormal heart rhythm

How soon will I recover?

You should be able to go home the same day.

You should be able to return to normal activities after about 2 days.

Regular exercise should improve your long-term health. Before you start exercising, ask the healthcare team or your GP for advice.


Atrial fibrillation can cause you to get palpitations and feel breathless, and increases the risk of a blood clot developing in your heart. Having an external cardioversion may improve your symptoms by giving you a shock to make your heart beat normally again.


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Last reviewed: September 2023

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