Assessment of regional myocardial perfusion and glucose uptake with positron emission tomography (PET) identifies dysfunctional myocardium that shows improvement in function after revascularization. Yet little is known about the ultrastructural patterns of ischemic injury in myocardium with and without postoperative functional improvement in relation to residual perfusion and metabolism. Therefore dynamic PET with [13N]ammonia and 18F-labeled deoxyglucose was performed in 24 patients with coronary artery disease and anterior wall dysfunction undergoing bypass surgery. Transmural biopsies were obtained from the dysfunctional area during surgery and analyzed by optical and electron microscopy to quantify the presence of fibrosis and cardiomyocytes. As judged from the postoperative changes in contraction, left ventricular function improved in 16 patients. In myocardium that showed improved function after revascularization, preoperative flow and glucose uptake were higher by PET than in persistently dysfunctional myocardium. In tissue samples from myocardium that improved postoperatively, there were more cardiomyocytes, including a larger proportion of cells with excess glycogen stores (35 vs. 21%), and there was less fibrosis (24 vs. 49%) than in tissue samples from myocardium that did not improve functionally. Preoperative perfusion and postoperative wall motion were inversely correlated with the amount of tissue fibrosis, whereas preoperative 18F-labeled deoxyglucose uptake correlated positively with the amount of cardiomyocytes showing excess glycogen stores.