We propose a comparison between between our standard ACT based heparin management protocol for children undergoing CPB and a patient-specific heparin concentration-based heparin management protocol. We hypothesize that a heparin concentration-based anticoagulation management protocol during CPB in children will result in more effective attenuation of hemostatic activation as reflected by decreased levels of thrombin formation and, ultimately, better preservation of hemostasis postoperatively.