Fatty substances such as cholestrol and saturated fats may be deposited on the inner surface of the coronary arteries. This narrows the lumen of these arteries and increases blood pressure. Such an affected artery develops a rough inner surface. This increases the risk of a blood clot being trapped in the artery. A blood clot that forms in an artery is called a thrombosis. Blood supply to the heart muscles can be greatly reduced due to the blockage of the coronary arteries. This can cause a heart attack. Hope this helps!