Newborns with congenital heart disease (CHD) are at increased risk of developing postpartum and postoperative blood clots after cardiac surgery. The molecular mechanisms that are responsible for the clotting profile predisposing children to blood clots in the early stages of life are currently not well described. The goal of this proposal is to prospectively collect plasma samples from ten (10) neonates with antenatal diagnosis of severe congenital heart disease (CHD) to better understand mechanisms responsible for abnormal clotting in the perioperative period.