A dose-finding pilot study including six patients concluded that isradipine at an initial rate of 0.6 microgram/kg/minute, decreasing to 0.3 microgram/kg/minute with further adjustments as necessary, was safe for the treatment of post-aortocoronary bypass graft hypertension. A comparative study followed, comprising 20 patients randomly assigned to receive isradipine (starting at 0.6 microgram/kg/minute) or nitroprusside (initially 1 microgram/kg/minute) for the treatment of post-aortocoronary bypass graft hypertension. Both drugs produced a satisfactory reduction in arterial blood pressure accompanied by a decrease in systemic vascular resistance. Central venous pressure and mean pulmonary artery pressure decreased with nitroprusside, but both increased with isradipine. Pulmonary capillary wedge pressure was reduced, heart rate increased, and cardiac output was minimally changed with nitroprusside. However, wedge pressure was maintained with isradipine and there was no tachycardia. An increase in cardiac output was seen, associated with an increase in stroke index. Isradipine is a more specific treatment for post-aortocoronary bypass graft hypertension than nitroprusside because its systemic arterial dilating effect is associated with a minimum of other circulatory changes.