Iloprost is a chemically stable derivative of carbaprostacyclin. We studied its hemodynamic effects in 10 patients in an intensive care unit. Iloprost was infused intravenously for 3 days for the treatment of advanced obliterative arterial disease of the lower extremities. Clinically significant hemodynamic responses were obtained with an infusion rate of 0.5 ng/kg/min. All subjects tolerated the dose of 4 ng/kg/min, which increased heart rate an average of 11% and cardiac index an average of 26%. This infusion rate decreased mean arterial pressure by 15%, total peripheral resistance by 31%, and pulmonary vascular resistance by 34%. Mean pulmonary arterial pressure, pulmonary capillary wedge pressure, left and right ventricular stroke work indices, and rate pressure product did not change. At higher doses of up to 8 ng/kg/min, responses were augmented only slightly, but side effects such as headache, nausea, and abdominal colics became more prominent. The data show iloprost to be a potent vasodilator that reduces both pre- and afterload and presumably induces a compensatory increase in cardiac output and heart rate, but does not increase the work load or oxygen demand of the heart.