Desmopressin acetate is used to reduce blood loss after cardiac surgery. However, there have been reports that hypotension can occur with infusion of desmopressin and that postoperative blood loss is not reduced. In this randomized, double-blinded study, we investigated the effects of desmopressin on hemodynamics, coagulation, and postoperative blood loss in patients undergoing primary elective coronary artery bypass grafting (CABG). After reversal of heparin effect, 20 patients received desmopressin 0.3 micrograms.kg-1, infused over 15 min, and 20 patients received a placebo. Desmopressin produced a small but significant decrease in diastolic blood pressure when compared with the placebo (50.8 mmHg vs. 57.6 mmHg for the desmopressin- and placebo-treated groups, respectively; P = 0.0372). A 20% or greater decrease in mean arterial pressure was observed in 7 of 20 patients receiving desmopressin, whereas only one patient in the placebo-treated group experienced a decrease of this magnitude (P = 0.0177). Reductions in arterial pressure were secondary to decreases in systemic vascular resistance (SVR) (mean SVR before and after the drug infusion, 1,006 and 766 dyn.s.cm-5, respectively, for the desmopressin-treated group; and 994 and 1,104 dyn.s.cm-5, respectively, for the placebo-treated group; P = 0.0078).(ABSTRACT TRUNCATED AT 250 WORDS)