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Cardioversion is a procedure that is used to help return your heartbeat to its normal rhythm if you have arrhythmia (irregular heartbeat). This information focuses on the type of cardioversion called electrical or direct-current (DC) cardioversion. We will just refer to this as cardioversion throughout.

You will meet the doctor carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.

Cardioversion is a procedure that uses an electric shock delivered from a defibrillator to restore your heart rhythm to normal if you have arrhythmia. Arrhythmia is caused by faulty electrical signals in your heart. There are different types of arrhythmia that can be treated with cardioversion. These include atrial fibrillation and ventricular tachycardia.

Ventricular tachycardia can be life-threatening, so cardioversion is often done urgently to correct your heart rhythm.

For other types of arrhythmia, cardioversion is usually given if your arrhythmia has lasted longer than 48 hours but less than a week. However, it can be difficult to know how long you have had your arrhythmia because in many people there are no symptoms.

Cardioversion isn’t suitable for everyone. It will depend on how long you have had arrhythmia for, your general symptoms and your medical history.

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  • Preparation Preparing for cardioversion

    Your doctor will explain how to prepare for your cardioversion.

    If you need to have cardioversion urgently, your doctor will give you an anticoagulant medicine, such as heparin. This is often given intravenously, which means you will have a drip inserted into a vein in your hand or arm to give you the medicine. You may also need to have a transoesophageal echocardiogram to scan for blood clots in your heart.

    If you have had arrhythmia for more than 48 hours, your doctor will plan your cardioversion at least three weeks in advance. This means there is enough time for any medicines your doctor may prescribe you to work properly. Your doctor may prescribe:

    • anticoagulant medicines – these help to stop your blood clotting (usually warfarin is used)
    • antiarrhythmic medicines – to help regulate your heart's rhythm

    You're likely to have the following hospital tests before cardioversion.

    • Blood tests – to check your blood count, how well your kidneys work and how well your blood clots.
    • Electrocardiogram (ECG) – this measures the electrical activity in your heart to see what your heart rhythm is.
    • Echocardiogram – this is an ultrasound scan of your heart, which provides a clear image of your heart muscles and valves to show how well your heart is working.
    • Transoesophageal echocardiogram – this uses an ultrasound sensor passed into your oesophagus (the pipe that goes from your mouth to your stomach) to take a scan of your heart. It's done if you're unable to take anticoagulant medicines or if you have only developed arrhythmia within the last few days.

    Cardioversion is routinely done as an outpatient or day case, under general anaesthesia. This means you will be asleep during the procedure and can usually go home the same day.

    If you're having a general anaesthetic, you will be asked to follow fasting instructions. This means not eating or drinking, typically for about six hours beforehand. However, it’s important to follow your doctor’s advice.

    Your doctor will discuss with you what will happen before, during and after your procedure, and any pain relief you might need. This is your opportunity to understand what will happen, and you can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead – you may be asked to sign a consent form.

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  • Alternatives What are the alternatives to cardioversion?

    There are many other treatments available to help regulate your heart's rhythm. Some are listed below.

    • Antiarrhythmic medicines – usually given as tablets – can help to control your heart rate and rhythm, but these may take several days or weeks to have an effect.
    • Ablation – this is a procedure in which tissue that may be disrupting the electrical signals in your heart is removed by freezing or burning it away.
    • Having a pacemaker fitted – a pacemaker is a device used to regulate your heartbeat. You may need to have a pacemaker fitted if your natural pacemaker isn't working properly.

    Your doctor will advise which treatment is most suitable for you.

  • The procedure What happens during cardioversion?

    Cardioversion usually takes five to 10 minutes after you’re given the general anaesthetic. Once you’re asleep, your doctor will give you a brief, controlled electric shock to your heart, usually through two pads placed on your chest that come from a defibrillator device.

    Your heart rate and rhythm is monitored throughout the procedure, so your doctor can see immediately if the procedure has reset your heart to its normal rhythm.

    Your doctor may give you up to two more electric shocks to reset your heart if the first attempt is unsuccessful.

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  • Aftercare What to expect afterwards

    You will need to rest until the effects of the anaesthetic have passed. This will likely be less than an hour.

    Your nurse will regularly check your heart rate and blood pressure. You will be able to go home once your heart rhythm is stable and you have fully recovered.

    Your doctor will prescribe anticoagulant and antiarrhythmic medicines for you to take at home. It’s important to continue taking anticoagulants for at least one month after cardioversion.

    You will usually be given a date for a follow-up appointment before you go home.

    You will need to arrange for someone to drive you home. After general anaesthesia, you should try to have a friend or relative stay with you for the first 24 hours. General anaesthesia temporarily affects your co-ordination and reasoning skills, so you must not drive, drink alcohol, operate machinery or sign legal documents for 24 hours afterwards. If you're in any doubt about driving, contact your motor insurer so that you're aware of their recommendations and always follow your doctor's advice.

    Contact your GP if you feel any changes in your heartbeat. If your arrhythmia has come back after you have had cardioversion, you may be able to have another cardioversion or alternative treatments to restore it – however, your doctor probably won't be able to give this to you straight away. For more information, see our frequently asked questions.

  • Risks What are the risks?

    Cardioversion is commonly performed and generally safe. However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications.

    As with every procedure, there are some risks associated with cardioversion. We have not included the chance of these happening as they are specific to you and differ for every person. Ask your doctor to explain how these risks apply to you.


    Side-effects are the unwanted, but mostly temporary effects you may get after having the procedure, for example, feeling sick as a result of the general anaesthetic. After having cardioversion, the skin on your chest may feel a little sore where the shock was administered.

    Cardioversion can cause a temporary drop in blood pressure, so you may have a headache or feel dizzy.

    The antiarrhythmic medicine amiodarone can cause problems with your thyroid gland, lungs and liver, and may make your skin very sensitive to sunlight. If you're prescribed amiodarone, you will have regular check-ups and will need to wear sunscreen and cover up in the sun more than usual.


    Complications are when problems occur during or after the procedure.

    The most common complication of cardioversion is failure to restore your normal heart rhythm. The success of cardioversion depends on your medical condition. Research shows cardioversion immediately restores the heart's normal rhythm in nine out of 10 people with arrhythmia. However, some people find that their arrhythmia returns again within a few days, and up to half of people treated with cardioversion have arrhythmia again within the first year. If your arrhythmia does return after treatment, you will usually have to take antiarrhythmic medicines for four weeks before and four weeks after having a repeat cardioversion.

    There are other possible complications of cardioversion. You could have an unexpected reaction to the anaesthetic. This is a problem for any procedure where anaesthesia is required and isn’t specifically related to cardioversion. You will be given medicines to help if this happens, but it’s extremely uncommon for such a short procedure.

    You may develop other problems with your heart rhythm during cardioversion, for example, your heart may beat unusually slowly or fast. You will be given medicines to help if this happens.

    There is an extremely small risk of having a heart attack or stroke after cardioversion. This happens when a blood clot which has formed in your heart is released during cardioversion, and then blocks the blood vessels in your heart or brain. Blood clots are more likely to form if you have had arrhythmia. You will be given anticoagulant medicines before your procedure to reduce your risk of blood clots forming. You will be advised to continue taking anticoagulant medicines for at least four weeks after your procedure to reduce blood clot formation.

  • FAQs FAQs

    Why do I need anticoagulant medicines before having cardioversion?


    Anticoagulant medicines are prescribed to help reduce your risk of developing a blood clot in your heart.


    If you have arrhythmia, it means you have an irregular heart beat. As a result, blood may start pooling in the chambers of your heart and could form a clot. If a blood clot is released from your heart, it can block blood flow in the coronary arteries of your heart and cause a heart attack. If it moves through your bloodstream to your brain, it could cause a stroke.

    Your doctor will usually prescribe anticoagulant medicine (usually warfarin) to help reduce your risk of developing a blood clot. You will usually be asked to take this for at least three weeks before having cardioversion, during the procedure and for four weeks afterwards.

    If your cardioversion has to be carried out urgently, within the first 48 hours after the arrhythmia starts, you're likely to be given heparin through a vein in your hand or arm. This helps prevent any blood clots forming in your heart. If you have had arrhythmia for longer than 48 hours but you have not had a full course of anticoagulation, a transoesophageal echocardiogram can be carried out first. You will be sedated and have a tube passed into your oesophagus (the pipe that goes from your mouth to your stomach) to scan for blood clots in your heart.

    Why do I need medicines to help regulate my heart rhythm after cardioversion?


    Medicines to help regulate your heart rate and rhythm are usually prescribed if cardioversion doesn't work or your arrhythmia comes back after a previous treatment.


    Arrhythmia can return at any time after a successful cardioversion. Cardioversion restores your normal rhythm, but it doesn’t prevent arrhythmia returning again.

    Studies suggest that cardioversion is more likely to be successful and arrhythmia is less likely to reoccur if antiarrhythmic medicines, such as amiodarone and sotalol, are used. Antiarrhythmic medicines help control your heart rate and rhythm.

    You're more likely to be given antiarrhythmic medicines if cardioversion hasn't worked for you or if your arrhythmia returns after a previous attempt.

    You’re unlikely to be given these medicines before your first cardioversion attempt because of the possibility of side-effects. However, your doctor may recommend using them if he or she thinks cardioversion is less likely to work without medication. For example, cardioversion is less likely to be successful if you have had arrhythmia for a long time (more than 12 months).

    Is there a limit to how many times you can have cardioversion for arrhythmia?


    You're likely to be offered a second cardioversion treatment if your arrhythmia returns after a previous successful procedure. If your arrhythmia returns again, your doctor is likely to suggest alternative treatments to correct your arrhythmia.


    It's possible that cardioversion may fail to correct your heart rhythm. It's also possible that arrhythmia may return at any time after cardioversion.

    Cardioversion may be attempted again if a previous attempt has failed or if arrhythmia returns after a successful procedure.

    With your second treatment, your doctor will most likely prescribe you medicines to help control your heart rhythm to help prevent your arrhythmia returning.

    If your arrhythmia does return again, your doctor is likely to suggest alternative treatments to correct it. This may include a different medicine, or combination of medicines, or ablation. Ablation involves freezing or burning away the tissue in your heart that is causing your arrhythmia.

  • Resources Resources

    Further information


    • Abnormal heart rhythms. British Heart Foundation., accessed 10 May 2012
    • Overview of dysrhythmias (cardiac). BMJ Best Practice., published 2 March 2012
    • Synchronized electrical cardioversion. eMedicine., published 9 May 2011
    • Joint Formulary Committee. British National Formulary. 64th ed. London: British Medical Association and Royal Pharmaceutical Society of Great Britain; 2012
    • Camm A, Luscher T, Serruys PW (editors). The ESC textbook of cardiovascular medicine. 2nd ed. Oxford: Oxford University Press, 2009:1101–130
    • Assessment of tachycardia urgent considerations. BMJ Best Practice., published 26 September 2011
    • Atrial fibrillation: the management of atrial fibrillation. National Institute for Health and Clinical Excellence (NICE), June 2006.
    • Atrial fibrillation. Prodigy., published August 2009
    • Heart treatments. British Heart Foundation., accessed 10 May 2012
    • Ventricular tachycardia treatment and management. eMedicine., published 9 November 2011
    • Atrial fibrillation (AF). The Merck Manual., published January 2008
    • Cardioversion for atrial fibrillation. Atrial Fibrillation Association (AFA)., published April 2010
    • Cardioversion. British Heart Foundation., accessed 10 May 2012
    • Frequently asked questions. Arrhythmia Alliance., accessed 11 May 2012
    • Amiodarone 100mg Tablets. electronic Medicines Compendium (eMC)., published 2 April 2012
    • Mead G, Elder A, Flapan A, et al. Electrical cardioversion for atrial fibrillation and flutter. Cochrane Database of Systematic Reviews 2005, Issue 3. doi:10.1002/14651858.CD002903.pub2
    • European Heart Rhythm Association, European Association for Cardio-Thoracic Surgery, Camm AJ, et al. Guidelines for the management of atrial fibrillation. Euro Heart J 2010; 31(19):2369–429. doi:10.1093/eurheartj/ehq278
    • Defibrillation and cardioversion. eMedicine., published 19 January 2010
    • What are the risks of cardioversion? National Heart Lung and Blood Institute., published 1 June 2010
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