If your heart has an irregular (uneven) beat or is beating too fast, cardioversion is a way to restore a regular rhythm. Abnormal heart rhythms are called arrhythmias. There are two kinds of cardioversion treatment, one in which the doctor may give one or more medicines to bring back the regular heartbeat. This is called pharmacologic (chemical) cardioversion. Secondly, the doctors also restore regular rhythms by sending an electrical shock to the heart. This is called electrical cardioversion. If you have atrial fibrillation, blood clots can form in your heart's left atrium. Cardioversion may knock loose a blood clot in your left atrium. If the clot (embolus) travels to your brain, it can cause a stroke. To avoid this, the cardiologist may give you medicine to make your blood less likely to form blood clots. If your doctor gives you the medicine, you'll need to take it for 2 to 3 weeks before the procedure. Transesophageal echocardiography is often used to check for the presence of blood clots before this procedure. Synchronised electrical cardioversion is used to treat hemodynamically unstable supraventricular (or narrow complex) tachycardias, including atrial fibrillation and atrial flutter. It is also used in the emergent treatment of wide complex tachycardias, including ventricular tachycardia, when a pulse is present. Cardioversion is a medical procedure by which an abnormally fast heart rate (tachycardia) or cardiac arrhythmia is converted to a normal rhythm using electricity or drugs. Pharmacologic cardioversion, also called chemical cardioversion, uses anti-arrhythmia medication instead of an electrical shock.