This study assesses whether an appropriately designed asanguineous initial reperfusate effectively reduces the reperfusion injury following prolonged global ischemia and improves the recovery of cardiac performance after cardioplegic arrest. Forty-eight isolated perfused working rat hearts underwent two hours of hypothermic (15° to 18°C) ischemic arrest followed by 30 minutes of normothermic reperfusion. During ischemic injury, multidose cardioplegia was delivered at 30-minute intervals. The reperfusion solution under study was infused during the last 3 minutes of ischemia, just prior to release of the aortic clamp. The usual hemodynamic variables of this preparation (heart rate, aortic pressure, aortic flow, coronary flow, and stroke volume) were serially recorded and expressed as percent of recovery of control values. The influence of the concentration of Ca2+, pH, and buffer was more specifically investigated. A reperfusate containing 1 mM of Ca2+ was found to result in higher post-ischemic hemodynamic values than a Ca2+-poor (0.25 mM) reperfusate. The best functional recovery was provided by an alkalotic (pH 7.70 at 28°C), glutamate-enriched initial reperfusate, which, by 30 minutes of reperfusion, yielded a 93.5 ± 2.3% recovery of aortic flow versus 83.6 ± 1.8% in the control group receiving unmodified reperfusion (p < 0.01). We conclude that an appropriate composition of the initial reperfusate can improve the recovery of cardiac function significantly following two hours of cardioplegic arrest and that such an improvement can be achieved by an asanguineous reperfusate provided its composition is properly designed with respect to electrolytes, pH, and substrates. © 1984, The Society of Thoracic Surgeons. All rights reserved.