Conversion to sinus rhythm (cardioversion) is recommended to prevent the haemodynamic and thromboembolic complications of atrial fibrillation. Prior anticoagulation is compulsory except in emergencies. The duration of anticoagulant therapy depends on the terrain and chronicity of the arrhythmia. Cardioversion may be proposed for the majority of patients in whom it is thought that sinus rhythm can be maintained by appropriate therapy. It may be carried out pharmacologically by oral or intravenous antiarrhythmic therapy. Amiodarone is the drug of choice. Cardioversion may also be carried out by external or internal direct current shock. The success rate of external electrical defibrillation depends on the energy administered, the site of the electrodes and a number of factors related to thoracic impedence. Internal electrical defibrillation may be performed with an endocavitary catheter or by the oesophageal approach, with few complications. The main problem resides in maintaining sinus rhythm in the long term. When this is not possible, cardioversion is useless, and therapy to slow the cardiac rhythm should be instituted.