The ECG changes resulting from endocardial resection, with or without aneurysmectomy and coronary artery bypass grafting (CABG), are reported in 82 patients. Angiographic and surgical features and peak creatine kinase (CK) levels are correlated with ECG findings. Twenty-three of 82 patients (28%) had the following ECG changes postoperatively: decreased ST segment elevation = 3 (4%), loss of R wave amplitude = 4 (5%), increased R wave amplitude = 5 (6%), new Q wave = 4 (4%), axis shift greater than or equal to 45 degrees = 6 (7%), and new bundle branch block = 6 (7%). Five of six new cases of bundle branch block were left bundle type and resulted from resection of the inferoposterobasal and contiguous septal endocardium. ECG anterior infarction, anterior aneurysm, and anteroseptal endocardial resection were associated with a significantly lower incidence of postoperative ECG changes. Aneurysmectomy and the performance of CABG were not significantly associated with postoperative ECG changes, but more bypass grafts per patient grafted appeared in the group with postoperative ECG changes, suggesting that coronary artery disease may be more severe in that group. Peak CK did not correlate with postoperative ECG findings. We conclude that ECG changes occur infrequently after endocardial resection and that the factors responsible are not clear, although severity of coronary artery disease may be contributory. Left bundle branch block is a significant complication of inferoposterobasal resection, but complete heart block appears not to be. The diagnosis of myocardial necrosis is difficult in these patients.