Cardioversion is a procedure that converts certain types of abnormal heart rhythms (arrhythmias) to normal rhythms. There are two types of electrical cardioversion, internal and external. External cardioversion may be performed in an emergency situation (e.g., with a defibrillator) or in a nonemergency situation. The most common type of nonemergency external cardioversion uses mild electrical shocks that are carefully timed to stop an arrhythmia and restore a normal heartbeat. In addition, cardioversion may also be accomplished with medications. 

External, nonemergency cardioversion is usually performed on a scheduled, outpatient basis. During the procedure, the patient will receive either general anesthesia or a strong sedative, and therefore not feel any pain. The procedure has shown great success in correcting certain arrhythmias (e.g., atrial fibrillation) that have not improved with medication alone. Patients may need to continue antiarrhythmic drugs after cardioversion.