Fifty patients with ischaemic heart disease scheduled for coronary artery bypass surgery received either an enflurane or a halothane anaesthetic. The anaesthetic techniques were randomly assigned to the patients and consisted of induction with diazepam 0.5 mg·kg-1 and pancuronium 0.1 mg·kg-1 supplemented by nitrous oxide and oxygen (50:50). Enflurane in dosages of 0.5-1.5 volumes per cent and halothane 0.3-0.7 volumes per cent were administered to Group E (25 patients) and Group H (25 patients), respectively. The inhalation drug dosage was varied to maintain heart rate and systemic blood pressure within predetermined limits. The two patient groups (E and H) were compared with regard to myocardial damage (determined electrocardiographically and enzymatically) as well as by haemodynamic changes and adjuvant cardiovascular drug therapy. One patient in group H sustained a postoperative infarction detected by electrocardiogram and sustained CK MB release. There was no other unequivocal electrocardiographic evidence of myocardial infarction in either group and the myocardial damage estimated from CK MB curves was remarkably low and similar in both anaesthetic groups. Myocardial damage was estimated by CK MB maximum release (CK MB MAX) of 8.1 ± 1.00IU/1 (Group E), 7.8 ± 1.32IU/I (Group H), by area under the CK MB disappearance curve (CK MB AREA) of 144 ± 21.9 IU/1 x hr (Group E), 173 ± 32.9 IU/1 x hr (Group H), and by the accumulated CK MB or CK MB damage size (CK MB DS) of 10.S±1.79IU/1 (Group E), 10.3 ± 2.26 IU/1 (Group H). There was no release of CK MB before cardiopulmonary bypass in either group. There was no statistically significant difference between the two groups for myocardial damage, haemodynamics or adjuvant drug interventions. There was a trend toward greater use of vasodilators in Group H than in Group E. It is concluded that enflurane and halothane are associated with equally low levels of myocardial damage when used for anaesthesia in patients with ischaemic heart disease. The release of CK MB occurred following cardiopulmonary bypass and probably represents imperfect myocardial preservation. Patients with severely impaired ventricular function were not studied, and in these patients enflurane and halothane must be used judiciously. © 1980 Canadian Anesthesiologists.