We investigated the effects of aprotinin, a protease inhibitor, on isolated rat heart subjected to cardioplegia and global ischemia for 4 hours and then reperfused for 40 minutes. Before ischemia, hearts were perfused with either aprotinin 1x105KIU/L[Aprotinin group,n=8 or no aprotinin[control group,n=8 added to Krebs-Henseleite solution for 30 minutes. Hemodynamic and biochemical parameters such as heart rate, LVP, dP/dt, coronary flow and creatine kinase were measured before cardioplegia and after reperfusion 10,20,30,40 minutes. After completion of experiment, wet and dry heart weight were measured for tissue water and water content evaluation. On reperfusion, recovery of LVP of aprotinin group at each time point was significantly better than that of control group[p<0.05 , and of dP/dt at reperfusion 40 minutes[p=0.034 . No statistically significant differences in heart rate, coronary flow and CK were observed between the two groups, but aprotinin group seemed to have better recovery. No significant differences in tissue water and water content were observed between the two group.These results suggest that pretreatment of aprotinin is effective in myocardial preservation in prolonged hypothermic ischemia and reperfusion.