The present studies were undertaken to test the hypothesis that cadmium alters myocardial metabolism, producing effects on coronary blood flow. Hearts isolated from adult, male Sprague-Dawley rats were control-equilibrated and then treated with Cd (0.1-100 microM). Myocardial O2 consumption (MVO2), lactate production, contractile activity, and coronary flow were determined at regular intervals. Parallel experiments were also performed in hearts administered 0.5 mM KCN to compare the effects of cadmium on myocardial lactate release with that of a known inhibitor of mitochondrial respiration. Coronary flow decreased significantly in response to Cd. This effect was dose-related (ED50 = 0.4 microM Cd), achieving maximal levels within the initial 5 min of exposure and persisting thereafter. Cd treatment also significantly decreased myocardial contractile activity [ED50 = 2.4 microM Cd (+dP/dt)] and MVO2 in a dose-dependent manner. This latter effect was time-dependent with an ED50 value of 2.1 microM at 5 min, as compared to a value of 0.5 microM Cd at 30 min. Lactate levels measured in the coronary effluent were unaffected by Cd treatment, except at the highest dose. Collectively, the results of this study failed to support a metabolic mechanism as the basis for the observed changes in coronary flow in response to cadmium administration. Instead, these results suggest an alternative hypothesis that Cd disturbs coronary flow via a mechanism involving direct actions on the coronary vasculature.