Abstract: In order to determine adequate anticoagulation in patients with cyanotic heart disease during extracoreal circulation, we measures the activated clotting time （ACT） of whole blood in sixteen such patients during cardiopulmonary bypass, using two levels of heparin. The results indicate that the first time heparin level of 2mg/kg body weight is adequate for most of this type of cyanotic patients. This heparin level is considered save for cyanotic patients during extracorporeal circulation, and able avoid side effects irrespective of overdosage of anticoagulant.