heparin n 1: a polysaccharide produced in basophils (especially in the lung and liver) and that inhibits the activity of thrombin in coagulation of the blood; it (trade names Lipo-Hepin and Liquaemin) is used as an anticoagulant in the treatment of thrombosis and in heart surgery [syn: {heparin}, {Lipo- Hepin}, {Liquaemin}]