The efficacy and hemodynamic effects of urapidil, an arteriolar vasodilator, and isosorbide dinitrate, a venodilator, were compared, when used for blood pressure control during abdominal aortic surgery. Urapidil is an alpha-adrenergic receptor antagonist with serotonin-1A receptor-agonist activity in the central nervous system. Hemodynamic profiles were recorded before and after the administration of the study drug (+/- 10 minutes before aortic clamping), 3 and 10 minutes following aortic clamping, and before and 3 and 10 minutes following the removal of the aortic clamp. Arterial and mixed venous oxygen contents were compared. Both groups of 18 patients were similar with respect to demographic profiles, anesthetic technique, and perioperative fluid therapy. Identical heart rate and blood pressure profiles were obtained. In contrast to isosorbide dinitrate, urapidil produced a 17% (P < 0.05) increase in cardiac index as a result of a 30% (P < 0.001) decrease in systemic vascular resistance before placement of the aortic clamp. In patients treated with urapidil, cardiac index was higher (P < 0.05) 10 minutes after aortic clamping, before removal of the clamp, and 10 minutes later. The arterio-venous oxygen content difference decreased from 3.2 +/- 0.8 mL O2/dL to 2.4 +/- 1.0 mL O2/dL (P < 0.01) following urapidil, but did not change during the administration of isosorbide dinitrate. It is concluded that urapidil is an effective and safe drug for the prevention of the hemodynamic consequences of aortic clamping. Compared to a venodilator (isosorbide dinitrate), urapidil offers the advantage of improving cardiac output and oxygen delivery.