The hemodynamic response after an iv loading dose of amiodarone for resistant supraventricular tachyar rhythmias was studied in ten critically ill patients receiving a catecholamine infusion for shock. A loading dose of amiodarone, 3.7 to 5.0 mg/kg. was infused over 2 h while the catecholamine infusion dose requirements were monitored. There was a significant decrease in heart rate (mean 16%,p< .01), and an increase in stroke volume index (mean 29%,p< .01) and left ventricular stroke work index (mean 34%,p< .01). Cardiac index, oxygen availability index, and mean arterial pressure were not changed significantly. The reported adrenoreceptor antagonism of amiodarone did not change catecholamine dose requirements in this study. In nine of ten patients, sinus rhythm was achieved and maintained. The loading dose of amiodarone had no significant acute effect on plasma digoxin concentrations. Despite good arrhythmia control, mortality was high.