Protein C is a major physiological anticoagulant. It is a vitamin K-dependent serine protease enzyme (EC 3.4.21.69) that is activated by thrombin into activated protein C (APC). The activated form (with protein S and phospholipid as a cofactor) degrades Factor Va and Factor VIIIa. It should not be confused with C peptide or c-reactive protein or protein kinase C.The protein C pathway’s key enzyme, activated protein C, provides physiologic antithrombotic activity and exhibits both anti-inflammatory and anti-apoptotic activities. Its actions are related to development of thrombosis and ischemic stroke. The protein C pathway of the coagulation of the blood involves the influences of lipids and lipoproteins and the study of the strong epidemiologic association between hyperlipidemia and hypercoagulability.