Fifty patients undergoing isolated coronary artery bypass grafting procedures using a clear, cold cardioplegic solution, topical hypothermia, and reduced systemic flow for intraoperative myocardial protection were evaluated for myocardial injury by serial plasma creatine kinase–MB isoenzyme (CK-MB) measurements and electrocardiograms. Forty-one (82%) of the patients had three-vessel disease. Preoperative left ventricular contractility determined angiographically was normal in 13 patients (26%), mildly abnormal in 26 (52%), and moderately or severely abnormal in 11 (22%). The number of arteries grafted ranged from 2 to 6 (mean, 3.5). The mean duration of aortic clamping was 38.6 ± 1.6 minutes. There were no hospital deaths. Enzymatic and electrocardiographic (ECG) evidence of myocardial infarction occurred in 1 patient. Nonspecific ECG changes occurred in 16 patients (32%), and the electrocardiograms were unchanged in the remaining 33 patients (66%). In the 49 patients without ECG evidence of infarction, the mean peak plasma CK-MB value, which occurred 6 hours after the onset of cardiopulmonary bypass, was 7.9 ± 0.8 IU/L (standard error of the mean) and the mean integrated area 158 ± 19.5 IU/L × hours. There was no correlation between these CK-MB values and the extent of disease, number of arteries grafted, or the duration of myocardial ischemia. These data document a low incidence of perioperative myocardial injury with this technique, and can serve as a baseline for comparison with other techniques for intraoperative myocardial protection in this setting. © 1982, The Society of Thoracic Surgeons. All rights reserved.