While the antiarrhythmic effects of amiodarone are well-documented, its hemodynamic effects are not. We injected 5 mg/kg amiodarone i.v. in 16 patients undergoing coronary arteriography. Heart rate did not change. Aortic (systolic, diastolic and mean) and left ventricular (systolic and end-diastolic) pressures decreased significantly (p less than 0.01) at 5 and 15 minutes; systemic vascular resistance also fell significantly (p less than 0.05), while cardiac index increased slightly but significantly (p less than 0.05). Coronary vascular resistance decreased significantly (p less than 0.01) and coronary sinus blood flow rose in most patients, from a mean of 138 ml/min to 153 ml/min at 5 minutes (p less than 0.02); it then returned toward the control value at 15 minutes (mean 145 ml/min). Myocardial metabolism of O2 was normal and unchanged. Metabolism of lactate improved in five patients, remained unchanged in seven and deteriorated transiently in four. No undesirable hemodynamic and clinical side effects occurred when the drug was administered slowly. We conclude that amiodarone is a powerful systemic and coronary vasodilator. In addition to its present indications in the treatment of angina pectoris and arrhythmias, the drug might be very useful as an afterload-reducing agent.