Objective: In this study we aimed to investigate in the light of the literature the efficacy of the fresh frozen plasma (FFP) given before the initial heparinization on achievement of adequate heparinization against heparin resistance (HR) during cardiopulmonary bypass (CPB). Material and Method: After obtaining the consent of the patients and the consent the institutional ethics committee, total of 50 patients older than 18 years old who had undergone cardiopulmonary bypass were enrolled to this study. Patients were randomly divided into two groups of 25 patients. The patients with liver and kidney failure were excluded from the study. The body weights, ages and the ACT values of the patients before heparinization were recorded. The group of patients given 2 units "Fresh Frozen Plasma" 15-30 minutes before heparinization was called the 'Group W' (Study Group), a group of patients who hasn't given FFP was called 'Group C' (Control Group). Four minutes after application of the first dose of heparin (Nevparin® 5000 İ.Ü./ mL heparin sodium), the control ACTs were measured (Actalyke Mini II ACT Analyzer Helena Lab.). The ACTs were repeated every half an hour and recorded. The patients with the value of ACT under 420 seconds were given additional doses of heparin according to their "Heparin dose-response curve". Results: The differences between the ages, body weights and the initial ACT values of the two groups were not statistically significant. The differences of the ACT values measured about 4 minutes after the first dose of heparinization between the two groups were statistically significant. This value was 650.74±244.81 seconds in the study group while in the control group it was found 505.92±159.78 seconds respectively (p = 0.018). The differences of the ACT values measured about 4 minutes after implementing the first dose of heparin were statistically significant between the two groups. Additional dose of heparin was required at about 4% of the patients in the study group and at about 24% of patients in the control group (p=0.042). Statistically no difference was observed between the two groups as for the additional need of heparin dose in the first half an hour. Conclusion: Since the diagnosis and treatment process is time-consuming and has a higher risk of death, especially in cases those who had to enter pump urgently and, in cases where ACT can not be measured frequently or the calibration of the measuring device of ACT in terms of reliability is suspicious, it was concluded that it is appropriate to give 2 units of FFP before full dose of heparinization in order to prevent heparin resistance or to make it more easily controllable.