(Level of Evidence B)  It is reasonable to maintain activated clotting time above 480 seconds during CPB. However, this min- imum threshold value is an approximation and may vary based on the bias of the instrument being used. For instruments using maximal activation of whole blood or microcuvette technology, values above 400 seconds are frequently considered therapeutic. (Level of Evidence C) Class IIb Recommendations  Use of a heparin dose-response formula may iden- tify reduced sensitivity to heparin, but has not been shown to be more useful than weight-based heparin dosing in determining the heparin dose required to achieve an adequate ACT for initiation of CPB. (Level of Evidence B)  Use of heparin concentration monitoring in addition to ACT might be considered for the maintenance of CPB, as this strategy has been associated with a signi cant reduction in thrombin generation, bri- nolysis, and neutrophil activation. However, its ef- fects on postoperative bleeding and blood transfusion are inconsistent. (Level of Evidence B)  During CPB, routine administration of unfractio- nated heparin at xed intervals, with ACT moni- toring, might be considered and offers a safe alternative to heparin concentration monitoring. (Level of Evidence C) Activated clotting time is considered the gold standard in monitoring anticoagulation for CPB. The establishment of a safe or optimal range for ACT dates back to data published in the 1970s when Bull and colleagues [3] showed no development of clot in the oxygenator or cir- cuit when ACT was maintained above 300 seconds. 