The nature of the enhanced blood fibrinolytic activity that evolved during extraacorporeal circulation was charaacterized by significantincrease or fibrin degradation product(FDP) in ECC group(P<0.01) but not in control group. The changes of protein C system also showed only in ECC group. The changes of protein C system were most pronounced in the early phase of cardiopulmonary bypass. The changes of FDP ane protein C system were observed in both bubble and membrane oxygenator-used group, but the pattern and degree of change were quite different (P<0.01), i,e., more severe in membrane oxygenator-used group.

These results confirm the disturbance of protein C system by extracorporeal circulation, which is possibly activated by the contact activation between blood and synthetic surface. So measurement of changes of protein C system could be used as a good method in the development of new materials for extracorporeal circulation.