"Fibrin is a protein found in the blood. Maintaining healthy levels of fibrin promotes healthy coagulation of blood for an optimally functioning cardiovascular system. Natto-K contains specialized blends of enzymes including Nattokinase with NSK-SD- the only form of nattokinase that does not contain Vitamin K2- to enhance the body's production of plasmin. Plasmin breaks down excess fibrin, which may improve circulation. Natto-K may help maintain already healthy levels blood clotting factors within a healthy range. "