The process of forming a thrombus, which is a solid mass or plug in the living heart or vessels composed of the constituents of the blood. Thrombosis usually occurs in a diseased blood vessel, as a result of arteriosclerosis. The consequences of thrombosis include local obstruction causing both tissue death and hemorrhage. Thrombosis is a significant factor in the death of an individual affected by arteriosclerotic cardiovascular disease, malignancy, and infection.