Protein C (PC) is a vitamin K dependent plasma protein that regulates coagulation by inhibiting FVa and FVIIIa and helps limit the extension of the thrombus. Numerous clinical studies have shown that a PC deficiency (acquired or congenital) is a risk factor for venous thrombosis. PC is a 62 kDa glycoprotein, synthesized by the liver in the presence of vitamin K. PC circulates in plasma in an inactive form, at a concentration of approximately 4 μg/mL. Thrombin bound to thrombomodulin loses its procoagulant properties and activates PC into activated PC. PCa in the presence of its cofactor, protein S, calcium and phospholipids, is capable of to inactivate the FVa and FVIIIa, true catalysts of coagulation, thus blocking the amplification loop of thrombin generation and limiting the extension of the thrombus.