Implantable cardioverter defibrillator

An ICD is a small device which can treat people with dangerously abnormal heart rhythms.

This video shows how ICDs and pacemakers are implanted:

Abnormal heart rhythms (or arrhythmias) can cause your heart to beat too quickly, too slowly or in an irregular pattern. These heart rhythms can happen suddenly and unexpectedly and sometimes people die as a result.

An ICD can give your heart electric pulses or shocks to get your heart rhythm back to normal.

The ICD is inserted just under your collar bone. It looks similar to a pacemaker and is a little bigger than a matchbox. It is made up of:

  • a pulse generator - a battery powered electronic circuit
  • one or more electrode leads which are placed into your heart through a vein

A new type of ICD is suitable for some people. It's called a subcutaneous (under the skin) ICD – or SICD for short. An SICD works in the same way as an ICD, but it's inserted just under the skin of the chest (outside of the ribcage) and there are no leads placed into the heart. Your doctor will talk to you about this option if it’s right for you.

How does an ICD work?

Your ICD constantly monitors your heart rhythm through the electrodes. If it notices a dangerous heart rhythm it can deliver the following treatments:

  • Pacing - a series of low-voltage electrical impulses (paced beats) at a fast rate to try and correct the heart rhythm
  • Cardioversion - one or more small electric shocks to try and restore the heart to a normal rhythm
  • Defibrillation - one or more larger electric shocks to try and restore the heart to a normal rhythm

Who needs an ICD?

You might need an ICD if:

  • you have already had a life threatening abnormal heart rhythm and are at risk of having it again
  • you haven’t had a life threatening heart rhythm, but you have had tests that show you are at risk of one in the future. This is usually because you have inherited certain faulty genes and may have a condition such as Cardiomyopathy, Long QT syndrome or Brugada Syndrome
  • you have another type of heart condition, such as heart failure, and have had or are at risk of having a life-threatening abnormal heart rhythm 
  • you have had other treatments to correct your heart rhythm which have been unsuccessful.
How an ICD is inserted

How is an ICD fitted?

ICDs are inserted under local anaesthetic, but with sedation, so you will feel very sleepy. It can take anything from one hour to three or more hours to implant an ICD, and the time it takes will depend on the type of device you're having. You will often (but not always) need to stay overnight in hospital and your ICD will be checked thoroughly before you leave.

Living with an ICD

It's very important to have regular follow-up appointments at your ICD clinic, so you can have your ICD checked. Your appointments may be every 3 to 12 months, depending on the type of ICD you have and if it has delivered any treatment. You will need to have follow-up appointments for the rest of your life.

You may have to make some changes to your lifestyle, for instance if you drive or take part in contact sports. You also need to be aware of how some electronic devices, such as TENS machines or airport security systems, can affect your ICD.

Your doctor will discuss these with you, and you can find out more in our ICDs booklet.

Who can I talk to?

It’s natural to feel worried about having an ICD fitted, but it often helps to talk about your feelings with someone close to you or with a healthcare professional.

If you have any questions, talk to your doctor or call our Heart Helpline on 0300 330 3311.

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Want to know more?

Order or download our publications:

Heart rhythms booklet

Heart rhythms


ICD - your quick guide

ICD - your quick guide

Leaflet / flyer