Possible enhancement of myocardial protection with oxygenated crystalloid cardioplegia and blood cardioplegia were evaluated in a cardiac enzyme study. The bicarbonate-containing solution equilibrated with 100% oxygen becomes highly alkaline as carbon dioxide is released. 95% oxygen and 5% carbon dioxide was added to the crystalloid cardioplegic solution [St. Thomas` Hospital No. 2 Solution] for prevention of severe alkalinity of oxygenated crystalloid cardioplegia. Heart was arrested and reinfused every 20 minutes throughtout the ischemic period with crystalloid cardioplegia or oxygenated crystalloid cardioplegia or blood cardioplegia. Group I was a patient with crystalloid cardioplegia in 11 patients. Group II was a patient with oxygenated crystalloid cardioplegia in 9 patients. Group III was a patient with blood cardioplegia in 15 patients. The value of CK-MB was evaluated from the patient`s serum at 6 hours, 24 hours, and 48 hours postoperatively. In Group I and II, there was no significant change of CK-MB. In Group I and III, the value of CK-MB at postoperative 6 hours was 114$pm$83 ng/ml and 56$pm$22 ng/ml [P < 0.05]. In conclusion, blood cardioplegia was superior to crystalloid cardioplegia.