Sixty-six consecutive patients with coronary artery disease were analysed in terms of myocardial lactate extraction during cardiac surgery. Sixteen patients had left main coronary heart disease and 50 were without such disease. Mean (s.d.) lactate extraction during empty beating in patients with and without left main coronary tract disease was -29.8(67)% and 12.0(15.3)%, respectively (P<0.001). No significant differences in lactate extraction were recognized during 15 min of reperfusion. Mean (s.d.) preoperative values of haemoglobin were 11.2(1.0) g/dl and these fell to 6.5(0.9) g/dl in an empty beating state during cardiopulmonary bypass (P<0.001). There was no significant difference between the two groups in preoperative and postoperative left ventricular stroke work index. An empty beating state before aortic clamping could induce unexpected ischaemia in the heart with left main coronary tract disease. A short duration of this ischaemic state does not influence functional recovery; however, exposing the left main coronary artery diseased heart to such a condition for long periods would be dangerous.