Where does heparin work on clotting cascade?

Heparin primarily works by enhancing the activity of antithrombin III, a natural anticoagulant in the blood. This interaction inhibits several key enzymes in the coagulation cascade, particularly thrombin (factor IIa) and factor Xa, thereby preventing the formation of fibrin clots. By inactivating these factors, heparin effectively slows down the clotting process and helps maintain blood fluidity.