Gradients of oxidative and glycolytic enzyme activities in the heart were studied by comparing samples taken from 10 locations from each of six bull hearts, within 30 min after slaughter. Citrate synthase (CS) was used as a marker of the oxidative potential and the lactate dehydrogenase (LD) subunits II and M as markers of aerobic glycolytic and anaerobic glycolytic potential respectively. CS activity in the ventricular tissue was greater than that of the right atrium, and no difference was found between the right and left ventricles. The left ventricular free wall had higher CS activity at the base than at the apex of the heart. Both the H and M subunit activities of LD increased in the following order: right atrium, right ventricle, ventricular septum, left ventricle. The left ventricular free wall showed higher H and M subunit activities at the base than at the apex. Within the left ventricular wall at the base, subendocardium had higher H and M subunit activities than subepicardium. The M subunit constituted the highest fraction of LD in the subendocardium and in the papillary muscle of the left ventricle. In conclusion, this study suggests that there are metabolic differences along both the radial and the longitudinal axes of the left ventricle and across the ventricular septum. These differences indicate that the greatest cellular stress, both aerobic glycolytic and anaerobic glycolytic in nature, occurs within the subendocardium at the base of the left ventricle and in the left ventricular papillary muscle.