Light micrograph (cross section) of an occluded (blocked) human coronary artery, caused by the narrowing of the artery (atheroma) & the subsequent development of a thrombus or clot (seen in the clear space). Coronary thrombosis, as here, leads to a heart attack or myocardial infarction. Deposits of fibrous tissue (stringy infill) on the sides of the arterial wall causes a degeneration of the wall & a narrowing of the lumen, or space, through which the blood flows. This condition is called atheroma. A complication of atheroma is the formation of a thrombus on the surface of the damaged tissue. It is seen here as yellow fragments in what remains of the lumen.