Formation of blood clots in coronary arteries is one of the major causes of cardiac arrest. Failure of the vessel to return to patency once a thrombus has formed leads to devastating consequences. Thus, we seek to understand the process of clot retraction and the role that platelet ProteinS (PS) plays in the fine balance between activation and quiescence of platelets. PS, a natural anticoagulant, is mostly secreted by the liver, but secretion directly from activated platelets has also been observed. The role of platelet PS has been unclear up until this time, and we hypothesize that it is involved in enhancement of clot retraction, in addition to its quint essentially role in inhibition of the clotting cascade. We try to find out that which domain of PS plays role in clot retraction and what is the mechanism still the mechanism is unknown.Â