Atherosclerosis is an aging process, which results in the hardening of arteries due to the deposition of cholesterol, lipids, blood cells etc. on the inner side of an artery. This is an age-related process. In this, the arteries harden and narrow. The process begins in early childhood in everyone, but progresses slowly in some people and rapidly in the others. When this happens within the coronary arteries, the person is at risk of a heart attack.

Gradually these fatty plaques grow; the lumen, the space inside a tubular structure of the coronary arteries, becomes narrow and the heart does not get enough blood. The  patient experiences chest pain and discomfort. This is called Angina Pectoris. In the beginning,  the pain is present only on exertion such as carrying loads or climbing up steps. Later it may occur even while resting.

Atherosclerosis gradually progresses and the lumen of the artery further narrows. When the narrowed lumen is completely blocked by further deposition of atheromatous (patchy) plaques or by a blood clot, the patient suffers a heart attack.

Gradual Blockage preferable
A gradual narrowing of the coronary arteries is preferable as this gives time to alternative arteries (called collateral arteries) to become functional, and supply blood to the deprived parts.

Sometimes, a small plaque may rupture inside the lumen of the coronary artery due to high BP, stress, the effect of nicotine in tobacco, heavy exercise or extreme excitement. The normal inner lining of the blood vessel is lost which encourages blood clot formation and the artery may be completely blocked suddenly. Such events lead to heart attacks, many of which are severe.

Although, atherosclerosis cannot be prevented its progress can be slowed by maintaining the blood cholesterol levels strictly within normal limits. This can be done by diet control, exercise and medicines.