Recent evidence suggests that postischemic contractile dysfunction of viable myocardium salvaged by reperfusion ("stunned myocardium") may be a consequence of abnormal calcium flux within the previously ischemic cells. Calcium channel blocking agents have been shown to enhance contractile function of stunned postischemic tissue, but it is not certain whether these improvements in function are due to the profound hemodynamic and vasodilator effects of these agents or to a direct effect on calcium flux within the stunned myocytes. Therefore, the effects of 1) high doses of nifedipine, given intravenously at 30 min after reperfusion, and 2) minute doses of nifedipine, infused directly into the coronary circulation at 30 min after reflow, were assessed and compared in anesthetized open chest dogs subjected to 15 min of transient coronary artery occlusion. As anticipated, intravenous nifedipine significantly reduced arterial pressure and increased regional myocardial blood flow. In addition, intravenous nifedipine restored systolic contractile function of the stunned, previously ischemic tissue to essentially normal preocclusion values: segment shortening averaged 102 ± 8% versus 26 ± 11 % of baseline at 2 h after treatment in treated versus control dogs, respectively (p < 0.003). Low dose intracoronary infusion of nifedipine did not alter hemodynamic variables or myocardial blood flow, but did improve segment shortening (90 ± 9% versus 37 & 10% of preocclusion values at 1 h after treatment versus 25 min after reperfusion [that is, pretreatment], respectively; p < 0.03). These data indicate that the calcium channel blocking agent nifedipine, given 30 min after reperfusion, enhances systolic contractile function of postischemic stunned myocardium. Because these improvements in function could be obtained even in the absence of systemic hemodynamic or coronary vasodilator effects, the data suggest that nifedipine may act by favorably modulating calcium flux within the stunned myocytes.