Heparinisation : The patient should be fully heparinised before the start of cardio pulmonary bypass. Baseline activated clotting time is measured (ACT). 3 mg (300 units) per kg body weight of heparin is administered. After five minutes, ACT is checked. It should be above 400 seconds for safe cardio pulmonary bypass. Heparin is added to the priming fluid in the pump, at the rate of 3 units per ml of fluid. During perfusion, ACT is checked every 15 minutes, to keep it above 400 seconds at 30°C and at 480 seconds, if the temperature is below 30°C. At the end of surgery, when the pump is switched off and the venous cannulae are removed, protsunine sulphate is given to neutralize the effect of heparin. The usual dose is 1 to 1.5 milligrams of protarnine sulphate for each milligram of heparin administered.