It is the most common arrhythmia in the clinical practice. It may be seen coincidentally in many patients presenting for both elective and emergency anesthesia. Alternatively, atrial fibrillation may occur for the first time during surgery. Ischemic heart disease is probably the most common cause of atrial fibrillation, followed by hypertension, rheumatic heart disease, thyrotoxicosis and pneumonia. Treatment of atrial fibrillation includes management of acute onset atrial fibrillation, maintenance of sinus rhythm, control of ventricular rate and prevention of thromboembolism. The immediate management of acute onset atrial fibrillation is usually cardioversion to sinus rhythm. The most reliable method is DC cardioversion. Postoperative AF usually occurs within the first 5 days of cardiac surgery, with a peak incidence on the day 2. Recent data suggest that once AF has occurred postoperatively, rhythm control by pharmacologic means or direct current electrical cardioversion offers little advantage to a rate control strategy.