To review the epidemiology, mechanisms, complications, predictors, prevention, and treatment of atrial fibrillation following cardiac surgery. MEDLINE search of English-language reports published between 1966 and 2000 and a search of references of relevant papers. Clinical and basic research studies on atrial fibrillation after cardiac surgery. Relevant clinical information was extracted from selected articles. Atrial fibrillation occurs in 10% to 65% of patients after cardiac surgery, usually on the second or third postoperative day. Postoperative atrial fibrillation is associated with increased morbidity and mortality and longer, more expensive hospital stays. Prophylactic use of beta-adrenergic blockers reduces the incidence of postoperative atrial fibrillation and should be administered before and after cardiac surgery to all patients without contraindication. Prophylactic amiodarone and atrial overdrive pacing should be considered in patients at high risk for postoperative atrial fibrillation (for example, patients with previous atrial fibrillation or mitral valve surgery). For patients who develop atrial fibrillation after cardiac surgery, a strategy of rhythm management or rate management should be selected. For patients who are hemodynamically unstable or highly symptomatic or who have a contraindication to anticoagulation, rhythm management with electrical cardioversion, amiodarone, or both is preferred. Treatment of the remaining patients should focus on rate control because most will spontaneously revert to sinus rhythm within 6 weeks after discharge. All patients with atrial fibrillation persisting for more than 24 to 48 hours and without contraindication should receive anticoagulation. Atrial fibrillation frequently complicates cardiac surgery. Many cases can be prevented with appropriate prophylactic therapy. A strategy of rhythm management for symptomatic patients and rate management for all other patients usually results in reversion to sinus rhythm within 6 weeks of discharge.