Heart surgery drug. Saline bag containing the anticoagulant drug heparin. An inflated air bag is being used to provide pressure and ensure a continuous supply of the drug into the patient's bloodstream. Heparin is an anticoagulant drug used during heart surgery to prevent the blood from clotting, both in areas where blood flow is stopped, and also in the heart-lung machine that takes over the function of the heart and lungs.