We compared the effects of 2 inotropic agents, dobutamine and isoproterenol on regional coronary blood flow, contractile function, hemodynamics and levels of phosphate compounds in the acutely ischemic canine heart. Dogs were instrumented to determine regional coronary blood flow (non-radioactive microsphere method), contractile function (sonomicrometry), and hemodynamics. Myocardial phosphate compounds were measured simultaneously by the phosphate-31 (31P) magnetic resonance spectroscopic technique. Both drugs augmented the global performance of the heart, but produced no significant improvement in regional contractile function in the ischemic region. Isoproterenol significantly increased the ratio of inorganic phosphate to phosphocreatine in the ischemic region, as compared to dobutamine. However, no significant differences were seen in myocardial lactate consumption with inotropic stimulation between the 2 groups. 31P magnetic resonance spectroscopy could be used to differentiate between the effects of dobutamine and isoproterenol on energy metabolism in ischemic myocardium despite the lack of significant differences in regional function and myocardial lactate consumption. The significant tachycardia without an augmentation of systemic blood pressure induced by isoproterenol may account for this unfavorable effect on myocardial energy metabolism.