This condition results when plaque builds up inside the coronary arteries that bring oxygen-rich blood to the heart muscle. When plaque (made up of substances such as fat, cholesterol and calcium) builds up in the arteries, it narrows them and reduces blood flow. The build-up of plaque (a condition called atherosclerosis) also makes the arteries stiff and inflamed, and increases the risk of blood clots that can partially or completely block blood flow. This form of heart disease can cause chest discomfort (angina), and lead to irregular heartbeat (arrhythmia) or cause a heart attack.