Three hundred and twelve elective adult coronary artery surgery patients were divided into five groups differing as to preoperative glucose or fat loading. The control group (n = 54) had a mean myocardial glycogen level of 880 mg/100 gram heart weight, a 18.5% incidence of serious ventricular arrhythmias, 24.2% dependence on vasopressors, a mean peak postoperative SGOT level of 100 IU, and a 3.7% perioperative transmural myocardial infarction rate. The 10% glucose loading group (n = 67) had elevated myocardial glycogen of 1180 mg/100 gram heart, 14.9% serious ventricular arrhythmias but a lessened dependence on vasopressors (17.9%), a peak post bypass SGOT of 74 IU, and 2.9% transmural infarction rate. A 20% glucose overnight loading group (n = 65) had myocardial glycogen level of 1270 mg/100 gram heart, a 23.0% incidence of serious ventricular arrhythmias, a significant reduction in vasopressor dependence (3.1%), no transmural myocardial infarctions, and peak post bypass SGOT of 53 IU. The intravenous fats (10% Intralipid) group (n = 57) had the highest glycogen level of 1509 mg/100 gram heart, the lowest peak SGOT of 51 IU, no infarctions, a low vasopressor dependence (5.2%), but high rate of serious ventricular arrhythmias (22.8%). The oral fat and 20% glucose loading group (n = 69) had a myocardial glycogen of 1486 mg/100 gram heart, a low vasopressor dependence rate of 4.3%, no infarctions, a peak SGOT of 66 IU, and the lowest serious ventricular arrhythmia rate of 4.3%. These results suggest that it is possible to alter prebypass myocardial substrate levels against the stresses of cardiac surgery with fat and/or glucose loading and that myocardial protection is evident.(ABSTRACT TRUNCATED AT 250 WORDS)