Despite controversial results concerning its effectiveness, cardiac surgical patients commonly receive desmopressin acetate (DDAVP) after cardiopulmonary bypass (CPB) in an effort to prevent or control bleeding diathesis. The side effects associated with DDAVP are usually considered benign. However, numerous authors have observed episodes of severe hypotension after DDAVP. As a part of a larger trial of DDAVP in routine first-time coronary artery bypass grafting (CABG), this randomized double-blind study of the hemodynamic effects of DDAVP was performed. Fifteen patients received DDAVP (0.3 microgram/kg over 15 minutes) and another 15 received saline placebo after skin closure. A statistically significant decrease in mean arterial pressure (MAP) was observed at 5 minutes after the beginning of DDAVP administration and the maximum decrease (mean change, -21 +/- 8 mm Hg, P less than 0.001) was reached as the infusion was completed. MAP did not change significantly in the control group. Hypotension after DDAVP was associated with a corresponding decrease in systemic vascular resistance. Postoperative blood loss was not different between the groups. It is concluded that routine administration of DDAVP to CABG patients is inadvisable because hemodynamic side effects are potentially dangerous and therapeutic benefit is highly unlikely.