This study examines heparin doses of patients having cardiopulmonary bypass supported surgery in terms of their sensitivity and resistance to heparin which is the standard anticoagulant used. The investigators use the Heparin Management System, an analyser that performs a heparin dose response test. In this test, a patient's whole blood is mixed with increasing amounts of heparin to determine the required dose to achieve a set level of anticoagulation. Patients who are found to resistant to heparin and needing a higher dose are thought by some to bleed more post operatively. It is my view that when the patient is given the correct amount of heparin which is then reversed by the correct amount of protamine (the reversal agent) the bleeding is not determined by heparin dose.