Formation of a blood clot (thrombus) in the heart or a blood vessel.
Contributing factors include injury to a blood vessel's lining from inflammation (thrombophlebitis) or atherosclerosis , blood flow that is turbulent (e.g., from an aneurysm ) or sluggish (e.g., from prolonged bed rest), or coagulation abnormalities (e.g., from high numbers of platelet s or excessive fat s in the blood). Thrombosis, especially in deep veins of the leg, is a particular danger after major surgery. A thrombus can block blood flow at the point of clot formation or break free to block it elsewhere ( embolism ).