Fibrin stabilizing factor (FSF) is a protein that is involved in the formation of a blood clot and stabilization of its structure. It is also called factor XIII or Trimaternal plasma. PSF is one of the important blood clotting factors, because it plays a key role in the beginning and completion of blood clot formation. Unfortunately, today's world is full of strokes and heart attacks, which often occur due to disruption of the blood coagulation system. A decrease in the level of PSF may be a factor provoking the occurrence of these pathologies. In this article we will look at why the balance of PSF is disturbed and how to change this condition.