Studies at necropsy have shown that the cardiomyopathy of Duchenne muscular dystrophy selects the posterobasal and contiguous lateral left ventricular (LV) walls as initial and primary sites of myocardial dystrophy in the absence of small-vessel coronary artery disease in these areas. The present investigation was designed chiefly to determine whether a myocardial metabolic abnormality could be identified in these same areas during a patient's life. Positron emission computed tomography was used to study regional LV metabolism with18F 2-fluorodeoxyglucose, and metabolism and/or perfusion was studied with13NH3. In addition, all subjects had the following performed: thallium-201 scans, technetium-99m multiple-gated equilibrium blood pool imaging, electrocardiograms, vectorcardiograms, and M mode and two-dimensional echocardiograms.18F 2-fluorodeoxyglucose activity was selectively increased in the posterobasal and posterolateral walls of the left ventricle in 11 of 12 patients with technically adequate images, indicating accelerated regional exogenous glucose utilization.13NH3 activity was selectively decreased in the same areas in 13 of 15 patients, indicating either a regional metabolic alteration in uptake and trapping, a reduction in regional blood flow, or both. These data identify a myocardial metabolic abnormality concentrated in specific segments of the LV free wall in living patients with Duchenne dystrophy.