Polarized light micrograph of heparin crystals, an anticoagulant and antithrombotic drug secreted by mast cells and basophils in the human body. It prevents coagulation by binding to and increasing the activity of antithrombin III, a plasma protein that inhibits thrombin and several other clotting factors. Thus, it prevents the polymerization of fibrinogen to fibrin and the subsequent formation of clots in the blood. It is prescribed for the prophylaxis and treatment of venous thrombosis, the prevention of post-operative deep venous thrombosis, pulmonary embolism and other clotting disorders, and to treat acute myocardial infarction and toxin-hepatitis. Additionally, it is used to prevent clotting in hemodialysis and hemofiltration, cardiovascular surgery, blood transfusions, and blood samples for laboratory tests, among others. Field of view size: 0.30 x 0.45 mm (0.012 x 0.018 in)