Ma HP, et al. - Among 195 adult patients undergoing cardiac valve replacement surgery, researchers explored the connection between individual heparin sensitivity and postoperative blood loss. Following initial heparin dosing (2.5 mg kg⁻¹), study participants were divided into three groups according to the whole blood activated clotting time (ACT): group A, insensitive group (ACT < 480 s); group B, sensitive group (480 s < ACT < 750 s); group C, hypersensitive group (ACT > 750 s). According to this prospective controlled study, postoperative blood loss is associated with heparin sensitivity in patients undergoing cardiac surgery, and the least postoperative bleeding is seen in moderately sensitive patients. Individual variation in heparin sensitivity is correlated with the mRNA and plasma levels of AT-III and factor X.