Patients with cyanotic congenital heart disease (CCHD) and associated secondary polycythemia are susceptible to develop coagulation abnormalities. Our study included one hundred patients with CCHD, 37% had TOF, 35% had TGA and other CCHD as TAPVR, single ventricle and pulmonary atresia. The age was between 4 days and 16 years. There was a statistically significant positive (direct) correlation between age, Hb% and HCT. Also, there was a statistically significant positive (direct) correlation between O2 and platelet count. We found that the indications of partial exchange transfusion were polycythemia, symptoms or both and it improved the platelet count so we recommend PET for patients with CCHD who are associated with secondary polycythemia, thrombocytopenia or other coagulation defects as a preoperative preparation for cardiac surgery because it will decrease the risk of postoperative bleeding in those patients. The study showed that patients with congenital cyanotic heart diseases may need pre and post operative management as vitamin k, FFP, platelet transfusion to improve the coagulation function and decrease the risk of post operative bleeding.