Patients who have undergone a Fontan procedure face an increased risk for thromboembolic complications. This study aimed to evaluate whether thromboelastography, a global whole-blood assay of coagulation, can be used to detect hypercoagulability in pediatric Fontan patients compared with healthy children. This prospective, cross-sectional study investigated 25 Fontan patients and 51 healthy children in three age groups: 1-5 years, 6-10 years, and 11-16 years. Kaolin-activated thromboelastography was performed on citrated samples. No statistically significant differences in thromboelastography parameters were found among the different age groups of the 51 healthy children. None of the 25 Fontan patients demonstrated evidence of hypercoagulability on thromboelastography (95% confidence interval, 0-7%), as defined by two standard deviations above or below the normal mean. The findings suggest that the percentage of Fontan patients demonstrating hypercoagulability on thromboelastography is substantially lower than the reported incidence of thromboembolic complications. Whether thromboelastography could be helpful in predicting patients at increased risk for thromboembolic complications or not still is not known. Further studies comparing the thromboelastography of Fontan patients with the thromboembolic complications of those without Fontan are needed to delineate these issues. © 2009 Springer Science+Business Media, LLC.