Children with cyanotic congenital heart diseases have a higher risk of bleeding or thrombosis. Rotational thromboelastometry, using tissue factor (EXTEM), a contact activator (INTEM), or cytochalasin (FIBTEM), assesses coagulation by determining the time to initiation of clotting (CT) and clot firmness (MCF), including platelet-fibrin-interaction. This study aimed to evaluate rotational thromboelastometry and whole blood impedance aggregometry in cyanotic congenital heart diseases (CCHD) compared with a control group without chronic cyanosis (NCHD) in a pediatric cohort. We prospectively included 200 patients (60 CCHD, 140 NCHD). Oxygen saturation in CCHD was 76% [70–85], and 98% [97−100] in NCHD (p