For comparison between groups, an assay using the hepcon machine to measure whole blood heparin concentration and an ACT will be obtained for each patient at the following intervals: after the initial heparin dose, 30 minutes after the initiation of CPB, the start of rewarming and immediately prior to the discontinuation of CPB. A sample for anti-factor Xa activity will also be obtained at each of the above time intervals to validate the heparin concentration determined by the hepcon machine to a laboratory measured value. Blood samples for biochemical markers of hemostatic activation will be collected from all patients before the initiation of CPB after the administration of the initial heparin dose and after the conclusion of CPB before protamine infusion. The following biochemical markers of hemostatic activation will be measured: prothrombin fragment 1.2, fibrinopeptide A, free tissue factor pathway inhibitor, factor V, factor VIII, and beta-thromboglobulin. The following measures of clinical outcome will also be recorded: amount of blood products transfused after protamine administration, time between the administration of protamine to leaving the operating room, 24-hour chest tube drainage, first post-operative weight, time to extubation and duration of ICU stay.