Pericardial adhesions following open heart surgery pose a special problems, increasing the risk of cardiac reoperation because of the danger of damaging the heart, coronary artery and veins, or grafts and also the fibrous tissue may obliterate the pericardial space and eventually constrict the heart. This study was undertaken to evaluate the effect of intrapericardial urokinase and dextran 40 on the formation of pericardial adhesions in an animal model. latrogenic traumas on the pericardium were surgically induced in 30 rabbits, simulating injuries possible during actual surgery. In all rabbits, blood [1 ml] was obtained from an ear vessel and injected into the pericardium. Control group of ten rabbits did not receive any further medication, urokinase group of ten received 15, 000-20, 000 IU of urokinase, and remained ten received 1 ml of 10% dextran 40. All rabbits were sacrificed at 4 weeks. At autopsy, the development of adhesions were graded as none [Grade I], minimal [Grade II], moderate [Grade III], and severe [Grade IV]. Histological studies of the parietal pericardium and epicardium were performed. The results were as follows: 1. Group 1[Control group] showed minimal adhesion in 40%, moderate in 50%, and severe in 10% of the group. Sharp dissections were necessary in 60% of adhesions. 2. Group II [Dextran group] showed no adhesions in 20%, minimal in 60%, and moderate in 20% of the group. 3. Group III [Urokinase group] showed no adhesions in 40%, minimal in 40%, and moderate in 20% of the group. Considering in this group, the adhesion activity was significantly suppressed [60% adhesions] compared to the control group [100% adhesions] [P < 0.05]. 4. Histological findings revealed mild serosal fibrosis in none adherent group, loose fibrous connections between two layers of pericardium in minimal adhesion group, tight fibrous connections in moderate adhesion group, and marked fibrous thickening and close attachment of two surfaces were noted in severe adhesion group. These data have revealed the decreased incidence of pericardial adhesions with urokinase and dextran 40.