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With time, these fatty plaques grow in size and harden, which may lead to a narrowing of the coronary arteries, somewhat like scale formation on the inside of a metal water pipe. When the coronary arteries become narrowed by more than 70%, the amount of oxygen reaching the heart muscle may not be enough to meet its demands. This inadequacy of blood supply become especially significant when the heart must work harder as during exercise, stress, after food etc. It is then that the heart muse cries out in pain, which is called angina pectoris.


If blood flow is completely blocked in the artery by a plaque, a blood clot (thrombus) forming within the narrowed artery, tr heart muscle supplied by this artery does not receive any bloc and starts to die. This leads to a heart attack. The blockage the artery can occur as the result of a gradual build up cholesterol within the artery over several years. A slow developing occlusion may give time for the heart to compensate for the blockage by the development of small alternate pathways called collaterals. These collaterals are a boon for the heart, and may even prevent a heart attack when this slowly narrowing artery finally occludes.

Another way that an artery may get blocked is when a small and often insignificant plaque becomes unstable and ruptures. Rupture of this unstable plaque may occur due to stress, excitement, exercise, or sudden rise of blood pressure. Plaque rupture results in a loss of the normal smooth lining of the arterial wall which in turn induces thrombus formation. Since the occlusion in this case is abrupt, there is no opportunity for collaterals to develop and the resultant heart attack is invariably larger than if t occlusion had been more gradual.