Objective: To assess the prophylactic effect of postoperative oral amiodarone on the incidence and severity of atrial fibrillation (AF) after coronary artery surgery. Design: Prospective, randomized, blinded, controlled study. Setting: University hospital. Participants: Patients who had coronary artery surgery (n = 200). Interventions: Patients in group 1 (n = 100) received oral amiodarone, 15 mg/kg, 4 hours after arrival in the intensive care unit, followed by 7 mg/kg/d until hospital discharge. Patients in group 2 (n = 100) received placebo. Measurements and Main Results: Incidence, duration, and recurrence of new episodes of AF and maximal ventricular rate response were recorded from day 0 until hospital discharge. Side effects related to arniodarone and complica- tions induced by new-onset AF were noted. The incidence of new-onset AF (12% v 25%) and maximal ventricular rate response (120 +/- 21 beats/min v 135 +/- 24 beats/min) were significantly lower in the amiodarone group. There were no side effects related to the administration of amiodarone. The incidence of complications induced by AF was comparable between the 2 groups. Conclusion: Postoperative prophylactic oral amiodarone after coronary artery surgery is safe and effective in reducing the incidence of new-onset AF and maximal ventricular rate response. Copyright 2002, Elsevier Science (USA). All rights reserved.