yyyy Adults with cyanotic congenital heart diseases (CCHD) have a higher risk for bleeding, but also for thrombosis. Rotational thromboelastometry (RT), 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. The aim of this study was to evaluate RT and whole blood impedance aggregometry (IA) in CCHD compared with a control group without chronic cyanosis (NCCHD). These were used to establish normal reference ranges. We prospectively included 124 patients (76 CCHD, 48 NCCHD). Mean oxygen saturation in CCHD was 81.5%, and 98% in NCCHD (p < 0.001). Fifty-five CCHD and 1 NCCHD had pulmonary hypertension. Eisenmenger syndrome was present in 39 CCHD (51.3%). Hemoglobin, hematocrit, and reticulocyte levels were significantly higher in CCHD, and they also showed more thrombocytopenia. Platelet aggregation was under normal range in 89.5% of CCHD after triggering with ADP, in 85.5% after triggering with arachidonic acid (ASPI) and in 73.7% after TRAP-6. RT showed significantly longer clotting times and reduced clot firmness in both EXTEM and INTEM tests. FIBTEM-MCF was also significantly reduced. Moderate inverse correlation was found between platelet count and erythrocytes (r = -0.608, p < 0.001). Significant correlations were found between platelet number and RT-parameters as well as with all IA parameters. In conclusion, according to RT and IA, CCHD present hypocoagulable disorders. No signs of hypercoagulability were found. (C) 2019 Elsevier Inc. All rights reserved.