Nitroglycerin (NTG) reduces the anticoagulant effects of heparin and may lead to heparin resistance. Fresh frozen plasma (FFP) and antithrombin III (ATIII) may be used for the treatment of heparin resistance. We aimed to compare the effects of FFP and ATIII on heparin requirement, coagulation parameters, and bleeding in patients undergoing coronary artery bypass graft surgery (CABGS) with moderate dose of intraoperative NTG infusion. Forty-eight patients undergoing CABGS with NTG infusion were randomly allocated to three groups. Group C served as control, whereas the patients in group P received FFP and those in group A received ATIII after anesthesia induction. ATIII activity and coagulation parameters were measured at five different times intraoperatively. Total heparin requirement, heparin consumption, and heparin sensitivity were calculated. ATIII activity and ACT were significantly higher and activated partial thromboplastin time and fibrinogen level were significantly lower during cardiopulmonary bypass in group A than in groups P and C. Heparin sensitivity was significantly higher and total heparin requirement and consumption were significantly lower in ATIII group than in other groups. ATIII administration increases heparin sensitivity and decreases heparin requirements compared with FFP in patients undergoing CABGS with peroperative NTG infusion. ATIII may be preferred to FFP in patients with heparin resistance due to NTG infusion undergoing CABGS. © 2011 Wolters Kluwer Health | Lippincott Williams &Wilkins.