Background The management of the coagulation system during pediatric cardiac surgery is a complex task. Cardiopulmonary bypass is a significant thrombogenic stimulus requiring anticoagulation with heparin prior to its initiation, and after the completion of the bypass period, reversal of heparin and the reestablishment of hemostasis prior to surgical closure. These manipulations toward both hypo- and hypercoagulability must be accomplished during the care of these children. The inability to attain either of these states within precise limits at specified points during the surgical procedure can have far-reaching implications. Adequate inhibition of the coagulation cascades is obviously necessary during CPB to prevent catastrophic clot formation in the CPB circuit. A state of partial, but inadequate, anticoagulation during this time can still prevent clot formation but will lead to the formation of coagulation products that can have deleterious effects on coagulation after CPB: thrombin is generated and subsequently activates plasminogen and the fibrinolytic system; fibrinolysis prevents the reestablishment of hemostasis and perpetuates the activation of the coagulation system; and thrombin, plasmin, and fibrin degradation products all severely disrupt post-CPB platelet function.