A study has been made of the haemodynamic affects of a single intravenous injection of amiodarone chorhydrate (5 mg/kg); the injection was given at rest to six normal subjects and six patients with coronary insufficiency due to atherosclerosis. The effects of the drug are most marked at the fifteenth minute after injection, and are: slowing of the heart rate; lessened cardiac output and left ventricular effort; a significant increase in mean pulmonary arterial pressure and diastolic pressure; slight variations in flow in the coronary sinus, with an increase in the ratio of coronary sinus flow to cardiac output. Amiodarone chlorhydrate appears to exert a favourable action upon the heart because, while it maintains myocardial perfusion, it tends to diminish the myocardial oxygen requirement by decreasing the rate of contraction and the contractility of the myocardium.