Cardioversion is a treatment that uses electrical energy to put your heart back into a normal rhythm. Using an external defibrillator, electrical energy (a shock) gets the heart back into sinus (normal) rhythm. We attach electrodes (sticky pads) to your chest to deliver the electric shock.

Cardioversion is very quick and can be very effective for many patients. For some patients, it helps them maintain sinus rhythm for several years, but this is not the same for everyone. It depends on how long you have been in atrial fibrillation (AF) for, and other factors such as how large your left atrium is.

Cardioversion and anticoagulants

Once you have your referral for cardioversion, you need to make sure that you have been taking your anticoagulant (such as warfarin or a NOAC). You need to be have been taking these for at least three weeks before the procedure.  


If you are taking warfarin, you need to have weekly INR levels between two and three. You will need to have these levels for at least three consecutive weeks leading up to your planned cardioversion. If the levels fall below two before your cardioversion, we will need to delay your procedure. This is because your risk of stroke increases.

After your cardioversion, continue taking your warfarin for at least fours weeks. If you have a CHA2DS2VASc score of less than one, you will need to take warfarin indefinitely. We will review this at your next clinic appointment.


If you are taking a NOAC (dabigatran, rivaroxaban or apixaban) you will need to take this as instructed for at least three weeks before your appointment. You must not miss any of the doses of your anticoagulant because this would increase your risk of stroke. If this happens, we would need to delay your procedure.

We don't routinely check on drug effects in patients taking a NOAC, so we recommend that you have a transoesophageal echocardiogram (TOE) before your cardioversion. This is to make sure that there are no clots. We do this by placing a probe in your oesophagus (food pipe) and taking an ultrasound scan of your heart.

If we find a clot in your left-atrial appendage, we will have to cancel your cardioversion procedure. Your TOE scan will be done in the same appointment as the cardioversion. You are under a general anaesthetic when this happens. You may find that your throat is quite sore after the TOE scan, which is normal. TOE scans are generally safe, but there can sometimes be damage to the food pipe (one in 5,000) or to teeth.

Continue on all your medications as normal unless you have been told otherwise. We may tell you to not take your beta blocker/calcium channel blocker on the morning of the cardioversion. This is to avoid bradycardia (slow heart rate) after the procedure.

The procedure

We will admit you to the day case unit/cardiology ward the morning of your cardioversion. You will then meet one of our doctors or clinical nurse specialists. They will take a full medical history, do blood tests including checking your INR levels and make sure that you are fit for the procedure.

We will do an ECG (electrocardiogram) to confirm that the arrhythmia is still present. We will then explain the procedure and ask you to sign a consent form. 

Once we have confirmed that you are ready for the procedure, we will take you to another department. You will meet the anaesthetist and a doctor/nurse who will explain what they are going to do. 

We will place two electrode patches on the upper right and lower left of your chest. These are then attached to the defibrillator. A cannula (small needle) is put into the back of your hand or in your arm. The anaesthetist will give you a short general anaesthetic to put you to sleep.

The defibrillator is then charged and ready to deliver a shock. One shock can be enough to restore sinus rhythm. But for a small number of people, they will need more shocks. Also for a small percentage of patients, they will remain in AF even after several attempts.  

Like any intervention, there are possible risks. These include:

  • Stroke - this is rare if INR levels have been within the therapeutic range of two to three for at least three consecutive weeks

  • Bradycardia - this is normally very brief following the cardioversion. A small percentage of patients may need intravenous medication or external pacing of the heart via the two electrodes that delivered the shock. In very rare cases, the patient may need to have a permanent pacemaker.

  • Ventricular tachycardia - this is rare but can occur following the initial shock. You would need a further shock to establish sinus rhythm.

  • Skin burns from the electrode pads - if this occurs, we will give you a cream to apply to the affected areas.

After the procedure

After your procedure, we will take you back to the day-case unit/ward to recover. We will track your progress for at least two hours before letting you go home. We will do an ECG before discharging you to make sure your heart is staying in sinus rhythm.

You will need someone to collect you, as you are not allowed to drive for 24 hours following this procedure. 

About three months after your cardioversion, you will come back for another clinic appointment. You will see either your doctor or clinical nurse specialist.

If your discharge ECG shows AF, we will book you back into the clinic earlier to discuss further treatment options.  

Atrial tachycardia is an abnormal heart rhythm which is usually seen in patients that have undergone heart surgery, have congenital heart defects or have undergone previous ablation procedures.

Atrial fibrillation is an abnormal heart rhythm. It is the most common heart rhythm disorder in the UK.

Contact our AF team

Harefield Hospital

01895 828979

Royal Brompton Hospital

020 7351 8364