The effect of verapamil administered before aortic cross-clamping was assessed in 40 patients undergoing elective coronary artery bypass grafting. Myocardial protection consisted of cold blood potassium cardioplegia, topical ice slush, and moderate (28 degrees C) systemic hypothermia. Patients were randomly divided into two groups: group 1 (18 patients) received verapamil (0.1 mg/kg up to 10 mg) intravenously three to five minutes before aortic cross-clamping; group 2 (22 patients) did not (control). Myocardial injury was assessed by cumulative release of the cardiac-specific isoenzyme of creatine kinase (CK-MB) after release of the aortic cross-clamp. Release of CK-MB was significantly lower in the verapamil group (44.9 +/- 6.2 versus 72.2 +/- 9.0 IU at 24.5 hours, p = 0.005). Calculated total infarct size was also lower in the verapamil group (6.0 +/- 0.9 versus 8.9 +/- 1.0 g-Eq, p = 0.035). Individual CK-MB release curves showed either one or two peaks. The two-peak pattern was more frequent in control patients (18 of 21 control patients versus 6 of 18 verapamil patients, p = 0.001) and was associated with a larger infarct size. Atrioventricular pacing was not required in any verapamil patient, but was needed in 1 control patient. We conclude that verapamil administered before aortic cross-clamping protects against myocardial injury during coronary artery bypass grafting with no increase in the incidence of atrioventricular block.