Additional 20 patients: These additional 20 patients will be enrolled to provide further validation of the Hepcon-measured heparin concentrations with the laboratory-measured heparin concentrations (anti-factor Xa activity). A blood sample will be obtained for a heparin dose response (HDR) assay prior to surgical incision Samples will also be obtained to measure a heparin concentration by the Hepcon machine and by anti-factor Xa activity at two time periods: after the initial heparin dose and immediately prior to discontinuation of CPB. In addition, these 20 patients will also have an ACT test analyzed by the Hepcon machine after protamine is given.