Atherosclerosis is the most common reason for blockage of blood vessels. Atherosclerosis occurs when fat and cholesterol build up on the inside walls of hardened arteries, similar to the way sludge slowly builds in a pipe. Cholesterol is a fatty substance normally made by the body. It is also found in the food we eat.

When this condition affects the coronary arteries it is called coronary artery disease. This build-up blocks or narrows the artery and prevents blood and oxygen from reaching the heart muscle. Slowed blood flow causes angina. Blocked blood flow causes a myocardial infarction (heart attack).

The amount and speed of this narrowing due to cholesterol deposits differs from person to person. It may go on for years without causing problems.