A 73-year-old female patient was admitted for myocardial infarction. Conventional treatment with heparin was started, intraaortic balloon assistance was required for several days, together with heparin. The platelet counts decreased progressively, from 288 G.l-1 on admission to 41 G.l-1 on the 16th day, despite the use of low molecular weight heparin. The in vitro heparin platelet aggregation test remained positive. This aggregation ended on adding iloprost, an analogue of prostacyclin, to the platelet culture bath. A coronary aortic bypass graft was required. An infusion of iloprost was started just after induction of anaesthesia. The initial dose of 0.5 ng.kg-1 x min-1 was gradually increased to 20 ng.kg-1 x min-1. Heparin (400 IU.kg-1) was thereafter added. To maintain a mean blood pressure of a least 50 mmHg, an infusion of up to 10 micrograms.kg-1 x min-1 of phenylephrine was given. As it was insufficient, an infusion of up to 1 microgram.kg-1 x min-1 noradrenaline was required. The iloprost infusion was gradually stopped 15 min before the end of CPB, together with that of noradrenaline. Platelet aggregation tests were positive after protamine had been given, whereas they had been negative during the infusion of iloprost. There was no abnormal postoperative bleeding. An infusion of 2 ng.kg-1 x min-1 was started at the sixth postoperative hour for 48 h, until the coumarin-like agent had started taking its effects. It is concluded that iloprost might be useful for carrying out cardiac surgery in patients with heparin-induced thrombocytopaenia.