Heparin can interfere with many aspects of the coagulation process and has an anticoagulant effect both in and out of the body. Its mechanism is complex, mainly through and antithrombin Ⅲ (AT - Ⅲ), and enhance the latter to activate Ⅱ, Ⅸ, X, Ⅺ and Ⅻ the inhibitory effect of clotting factors and its consequences involved in preventing platelet aggregation and destruction, inhibit the formation of blood coagulation activation of enzyme, blocking prothrombin into thrombin, inhibition of thrombin, thereby preventing fibrinogen to fibrin, which play a role of anticoagulation.