Heparin
Heparin, substance produced by cells of the liver, lungs, and intestines that keeps blood from clotting. It normally inhibits the clotting of blood by interfering with the production of thrombin, an enzyme necessary for clot formation. Heparin obtained from animals is administered after surgery to reduce the risk of thrombosis, the formation of a blood clot in a blood vessel. It is also used after pulmonary embolism to ensure that no further clots form, as well as during kidney dialysis.