Ischemia and subsequent reperfusion with 5.5 mM glucose or sodium acetate were studied for impact on energy metabolism of the guinea pig isolated heart and glutamate, aspartate, and alanine levels in it and myocardial outflow. Acetate reperfusion resulted in a more significant reduction in the pool of adenine nucleotides and total creatine (phosphocreatine + creatine) by 48 and 60% of the baselines, respectively than did glucose reperfusion (as much as 65 and 76% reduction, respectively). The total glutamate and aspartate pool was twice as less as the baseline after reperfusion with any of the substrates, with acetate, tissue glutamate concentration was decreased by 42% of the baseline, whereas with glucose, it was reduced by as much as 62%. The consumption of amino acids was largely associated with their implication in alanine synthesis, which was stimulated by glycolysis/glucogenolysis at the early stage of reperfusion. The residue glutamate and aspartate contents in the reperfused hearts positively correlated with the pool of adenine nucleotides, total creatine, and the recovery of myocardial contractility. The findings suggest that the myocardial levels of these amino acids are closely associated with its energy state following ischemia and thus may affect the recovery of cardiac contractility.