The purpose of this study was to assess the efficacy of clonidine in achieving perioperative hemodynamic stability in patients undergoing coronary artery bypass grafting performed under high-dose alfentanil anesthesia. Twenty-four patients with left ventricular ejection fraction greater than 0.5 were prospectively studied in a double-blind manner; those requiring emergency procedures were excluded. They were randomized to receive either oral clonidine or placebo together with their premedication. Induction of anesthesia was achieved with 10 mg of alfentanil infused over 5 minutes followed by a continuous infusion of 60 mg/h during 1 hour, or until sternotomy, and then 30 mg/h until the end of surgery. Hemodynamic responses to noxious stimuli were treated with additional alfentanil boluses and isoflurane when these were unsuccessful. Intraoperative hemodynamic profile analyses showed a continuous increase in systemic vascular resistance and mean arterial pressure in the clonidine group from the time of skin incision until the onset of bypass, whereas the cardiac output profiles remained similar in the two groups. The number of additional alfentanil boluses was similar. Isoflurane requirements (1/11 v 4/13) were not significantly different, but only a few patients required this therapy. The postbypass hemodynamic profiles were similar. Severe hemodynamic impairment occurred in the clonidine group during warming in the postoperative period: this group showed a drop in systemic vascular resistance index (1276 +/- 347 v 1757 +/- 415 dyn.sec.cm-5.m2) that could not be compensated for by an increase in cardiac output despite normal filling pressures, causing hypotension (66 +/- 10 v 79 +/- 16 mmHg). This hemodynamic status led to greater requirements for vasoactive agents and inotropics in this group.(ABSTRACT TRUNCATED AT 250 WORDS)