The aim of the study was to compare three anaesthetic agents in patients with ejection fraction below 0.40 subjected to coronary revascularization surgery. Twenty five elective coronary surgical patients with ejection fraction below 0.40 were prospectively studied. Premedication was pethidine 1 mg/kg and induction was fentanyl 0.03 mg/kg and pancuronium 0.1 mg/kg. The patients were randomized to one of three maintenance techniques (fentanyl, isoflurane or halothane). Radial arterial pressure, heart rate, right atrial pressure, pulmonary arterial and occluded pressures, and thermodilution cardiac output were measured, and cardiac index and resistance calculated, at the following times: before induction; 5 min after intubation; 2 min after sternotomy; immediately after discontinuation of bypass; 15 min afterwards; immediately after sternal closure; during suture of the skin; 5 min after arrival in the postoperative care unit; and 60 min postoperatively. Mean arterial pressure decreased significantly in the isoflurane group and nonsignificantly in the halothane group after induction. Cardiac index decreased significantly in the isoflurane group and nonsignificantly in the halothane group after induction and after sternotomy. Neither pressure nor flow decreased in patients receiving fentanyl. Following weaning from cardiopulmonary bypass, systemic vascular resistance decreased significantly in all groups. Cardiac index, however, did not increase above control values and arterial pressure consequently decreased; there was no significant difference between groups.