Book excerpt: 1.1. Definition of Terms-Thrombosis, Thromboembolic Disease, Atherosclerosis, and Blood Clotting The terms heart attack or myocardial infarction are more commonly used than thrombosis. The infarct-muscle destruction is simply the end result and thrombosis is the real cause of the heart attack. Thrombosis may be defined as the process of formation of a coalescent or agglutinated solid mass of blood components in the blood stream. Thrombi formed in either arteries or veins often cause occlusion in the vascular system and prevent blood flow. Obstruc to the blood vessel usually occurs at the site where the thrombi deposit. tion Furthermore, thrombi may break loose, travel through the circulating blood stream, and cause obstruction at some distal point of narrowing elsewhere. The mass or thrombus that moves is referred to as an "embolus." The two phenomena are lumped together under the term thromboembolic disease. Thrombosis that reduces blood supply to the heart is the primary factor in heart attacks.