Heparin was originally named after its discovery in the liver. It is a mucopolysaccharide sulfate ester composed of glucosamine, l-aldosteronism, n-acetyl glucosamine and d-glucuronic acid alternately, with an average molecular weight of 15KD and strong acidity. It also exists in lung, blood vessel wall, intestinal mucosa and other tissues, and is a natural anticoagulant substance in animals. Naturally occurring in mast cells, it is now extracted mainly from the mucous membranes of the lungs of cattle or the small intestine of pigs. As an anticoagulant, it is a polymer composed of two polysaccharides alternately linked and has anticoagulant effects in vivo and in vitro. Clinical mainly used for thromboembolic diseases, myocardial infarction, cardiovascular surgery, cardiac catheterization, extracorporeal circulation, hemodialysis and so on. With the development of pharmacology and clinical medicine, the application of heparin is expanding.

　　Pharmacological action: the ratio of activity to anticoagulant activity of low molecular weight heparin is 1.5 ~ 4.0, while that of ordinary heparin is 1, which not only maintains the antithrombotic effect of heparin, but also reduces the risk of bleeding. It has the advantages of long half-life and high bioavailability, and is widely used in the prevention and treatment of thromboembolic diseases. Its efficacy and safety are better than ordinary heparin, and the dose-effect relationship is clear. It is convenient to use a fixed dose without laboratory monitoring to adjust the dose.