Cardioversion (external)

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 heartbeat is controlled by electric impulses from a group of cells on your heart called the sinus node (see figure 1).

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.

Diagram of external cardioversion

What are the benefits of an external cardioversion?

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

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.

You may be able to have a catheter ablation. This uses heat to create scars that prevent the abnormal electric impulses from affecting your heart.

What does the procedure involve?

External cardioversion usually takes 10 minutes and is usually performed under a general anaesthetic.

The healthcare team will 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?

  • Soreness
  • Change in your heart rhythm
  • Low blood pressure
  • Fluid collecting on your lungs
  • Allergic reaction
  • Stroke

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 two days.

Do not drink alcohol or caffeine.

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.

Self-pay guide price

From £1,405


Self-pay package details

External cardioversion is performed at The Foscote Hospital by

  • consultant silhouette

    Dr Ian Arnold

    Consultant Cardiologist


    Learn more
  • Dr Joanna d'Arcy cardiologist

    Dr Joanna d’Arcy

    Consultant Cardiologist


    Learn more
  • Dr Nik Sabharwal

    Dr Nik Sabharwal

    Consultant Cardiologist


    Learn more


Author: Dr Julia Baron MD FRCP BMBS

Illustrator: Medical Illustration Copyright © Nucleus Medical Art. All rights reserved.

This page is intended for information purposes only and should not replace advice that your relevant health professional would give you.

Copyright © 2018 EIDO Healthcare Limited. The operation and treatment information on this website is produced by EIDO Healthcare Ltd and used under licence by The Foscote Hospital. The intellectual property rights to the information belong exclusively to EIDO Healthcare Limited. You may not copy, print out, download or otherwise reproduce any of the information other than for your personal, non-commercial use.