An anticoagulant is a pharmaceutical drug or natural substance that is used to prevent or treat blood clots, otherwise known as a Thrombus. Two common anticoagulant drugs are Heparin and Warfarin, which both act to prevent the clotting of blood in a vein or artery that may have lead to diseases such as deep vein thrombosis and pulmonary embolisms which could lead to fatality. Heparin is administered intravenously and therefore is used in an emergency to elicit a quick response, such as in atrial fibrillation. Warfarin is administered in a tablet form so can be taken at home, and can be used to prevent a blood clot from either forming or becoming larger. It works by reducing the amount of active Vitamin K in the blood, which is required for the mechanism of blood clotting factor VII and prothrombin. Anticoagulant is naturally found in salivary glands of anopheline and culicine mosquitoes. Anopheline mosquitoes have thrombin-directed anticoagulants while culicine mosquitoes have FXa-directed anticoagulants.