Patients with a particular thrombotic profile may be at greater risk of myocardial infarction during coronary artery bypass graft surgery. The thrombotic profile of 50 patients admitted to hospital with stable angina pectoris was determined prior to haemodynamic investigation. ECG results and determination of cardiac enzymes showed that 12 patients had suffered a perioperative myocardial infarction. These patients had a higher mean atherosclerotic score (42.1 +/- 10.5 vs 32.9 +/- 13, P less than 0.02), a longer aortic cross clamp time (59 +/- 15.2 vs 45.7 +/- 16.3 min, P less than 0.05), lower serum levels of protein C (101.2 +/- 26 vs 124.7 +/- 31.4%, P less than 0.05) and tissue plasminogen activator (322 +/- 580 vs 2307 +/- 2830 IU ml-1, P less than 0.01). There were no differences between the two groups in Jenkin's coronary score, the number and type of grafts, ejection fraction, left ventricular end-diastolic pressure, lipid profile or levels of markers of platelet release. In addition to a more severe distal coronary atheroma and a longer aortic cross-clamp time, patients with impaired endothelial fibrinolytic activity appeared to be at greater risk of myocardial infarction during coronary artery bypass graft surgery.