Objective:To investigate the reasons and treatment measures of heparin resisitance in patients undergoing cardiac surgery during cardiopulmonary bypass(CPB).Methods:Retrospective analysis of 1 258 patients undergoing cardiac surgery was made.Results: After 400 U/kg heparin was injected intravenously

the activated clotting time(ACT)could not be extended to 480 seconds or was shortened soon after extended to 480 seconds in nineteen patients(1.51%)including seven patients with cardiac myxoma

three patients with rheumatic heart disease

three patients with infective endocarditis patients

two cases of atrial septal defect patients

two cases of tetralogy of Fallot patients

one cases of ventricular septal defect patient and one cases of double outlet right ventricle patient.A large number of heparin was added to maintain ACT at safe range for anticoagulation.But it was invalid for five patients to add heparin

and then ACT could be extended to 480 seconds after 400～600 ml fresh frezon plasma or blood was transfused.Conclusion:Heparin resistance was commonly encountered in cardiac myxoma

infective endocarditis and cyanotic heart diseases requiring CPB.It was associated with the appearance of similar heparin mucopolysaccharide material in the blood

decrease of antithrombinⅢ(ATⅢ)content and activity

increase of platelet count

preoperative anticoagulant therapy and the use of contraceptives.ACT should be monitored frequently during CPB.