Effects of methylprednisolone were studied on isolated, blood-perfused cat hearts subjected to 1 hr of normothermic ischemic arrest. Untreated hearts sustained decreases in peak ventricular pressure pulse, dP/dt. and ventricular compliance. Ischemic hearts also became edematous, gained sodium, and lost potassium and creatine kinase enzyme activity. Steroid treatment did not significantly alter any of these ischemia-induced changes. Methylprednisolone treatment did increase resting coronary flow and also increased the hyperemic response after reperfusion. These results, in isolated hearts, provide no evidence that steroid treatment exerts a direct protective effect on the globally ischemic myocardium.