We measured indices of energy metabolism in tissue samples taken from the interventricular septum and left ventricular free wall of open-chest dogs under control conditions and after a 20-second period of no coronary inflow. The heart was paced at 150 beats/min, and arterial pressure was controlled by aortic constriction. Each tissue sample was divided into three transmural regions and analyzed for creatine phosphate, adenosine triphosphate, and lactate. Data were also obtained in animals subjected to ventricular fibrillation, with ventricular pressures reduced to atmosphere and sampling delayed to 70 seconds, and with the pulmonary artery constricted prior to coronary artery occlusion. In control animals, there were no metabolite differences between the free wall and septum. Coronary occlusion produced a lactate gradient across both the free wall and septum, with the highest lactate concentrations occurring in the regions adjacent to the left ventricular cavity. The increase in tissue lactate above control was greater in the septum than in the free wall. Coronary occlusion decreased tissue creatine phosphate but not adenosine triphosphate. The decrease in creatine phosphate was greater in the septum than in the free wall. Coronary occlusion and ventricular fibrillation, or coronary occlusion and ventricular pressures reduced to atmosphere, produced neither transmural metabolite differences nor differences between the free wall and septum. Pulmonary artery constriction increased right and decreased left ventricular pressures.(ABSTRACT TRUNCATED AT 250 WORDS)