Introduction:The aim of this study was to determine the effect of fresh frozen plasma (FFP) for priming of cardiopulmonary bypass (CPB) circuit on rotational thromboelastometry (ROTEM) and transfusion in pediatric cardiac surgery.Methods:Eighty patients younger than seven years old, were divided into case (FFP) (n=40) and control (n=40) groups. In the case group,10-20 mL/kg fresh frozen plasm was used for priming the CPB. The control group received 10-20 mL/kg of hydroxyethyl starch. ROTEM was done before surgical incision and after separation from CPB. The amount of transfusion (platelet and FFP) in the operating room and 24 hours after surgery were recorded.Results:Statistically significant difference was found between the case and control group in terms of changes in the Rotem parameters. The amount of transfusion of platelets in the operating room was significantly higher in the control group than in the case group.Conclusion:It seems that adding FFP to the prime solution is more effective in young patients and infants due to the higher susceptibility of the infant coagulation system to coagulation and hemorrhagic disorders in comparison with other patients.