Atherosclerosis is a form of hardening of the arteries in which plaque accumulates in the walls of arteries, eventually causing the opening of the vessels to narrow. When an artery becomes narrowed enough, the oxygen and nutrients carried by the blood cannot reach the organ supplied by that artery, starving it. For instance, the coronary arteries deliver blood to the heart. If the heart is not getting the amount of blood it needs—especially when it has to work harder, as it does during exercise or times of emotional stress—it is said to be ischemic. The term ischemia means a relative lack of blood supply. Hence, the terms ischemic heart disease (IHD), or coronary heart disease (CHD).
The symptom experienced by people whose hearts are being deprived of oxygen is called angina pectoris. Angina usually feels like a squeezing, burning, or pressure in the chest that is predictably brought on by exercise or emotional stress, and that goes away within about five minutes with rest, relaxation, or a medicine called nitroglycerin.
In addition to obstructing arteries to the point where blood flow is compromised, plaques can also rupture. A plaque that ruptures resembles an abscess or a boil in the wall of an artery. When the plaque material comes in contact with the blood flowing through that artery, the body tries to wall off this material by forming a blood clot (thrombus). If a clot forms over a ruptured plaque, blood flow through that artery can be completely interrupted, and the heart muscle downstream of the clot will die within a few hours if the circulation is not restored. Heart muscle damage from interruption of the blood supply is a myocardial infarction: a heart attack.