 1. Background: Heparin forms a complex with a plasma protein, antithrombin III ATIII is an endogenous anticoagulant. This complex inhibits the formation of thrombin and accelerates its destruction. In addition, heparin and ATIII inactivate other proteases of the coagulation cascade, especially the anti-activated factor X. The outcome of these biochemical actions is the inhibition of the formation and synthesis of activators of the clotting factors that exert critical functions in the genesis of the blood clot. Patients with chronic renal failure CRF that make use of hemodialysis need a system of anticoagulation with direct inhibitors of thrombin and or heparinoids to prevent thrombosis. 