Anticoagulants are substances that block the clotting reactions and thus stop the coagulation process. Ordinarily there are anticoagulants circulating in the plasma since under normal conditions the blood must be kept fluid. In Medicine anticoagulants like heparin are used in surgeries in which tissue injuries made by the surgical act could trigger undesirable systemic blood clotting. They are also used to avoid the formation of thrombus inside blood vessels of patients facing increased thrombotic risk.