In a group of 95 patients having cardiac operations with extracorporeal circulation, intravenous (IV) amiodarone, administered in doses of 2.5 to 5 mg/kg, was used in the treatment of various perioperative arrhythmias. Conversion to sinus rhythm was achieved in 55 (61%) of 90 patients with supraventricular arrhythmias, the other patients showing a satisfactory slowing of their heart rate. Total suppression and control was obtained in 18 patients with persistent ventricular extrasystoles associated with various supraventricular arrhythmias. Amiodarone was administered in five patients with life-threatening ventricular arrhythmias resistant to other antiarrhythmic agents: Suppression was obtained in one of two patients with recurrent ventricular tachycardias and control was achieved in three patients with repetitive ventricular tachycardia and ventricular fibrillation, allowing the effective use of intra-aortic balloon counterpulsation (IABP) needed for hemodynamic support. Seven patients experienced minor side effects such as nausea or flushing. No complete atrioventricular (AV) block was noted. Significant hypotension occurred at the end of the IV injection in 17 (18%) patients. In all but five patients, hypotenion was transient, without clinical complications. In the five others, adrenergic drugs in four cases and IABP in one case were necessary. Those five patients had marked cardiomegaly with poor myocardial contractility. IV bolus injection of amiodarone seems prohibited in such patients; constant infusion would be preferable.