Arteries are the pathways through which blood flows from the heart to the rest of the body. A thin layer of cells the endothelium line the arteries. The endothelium ensures the smooth flow of blood. But if there is any damage to the endothelium it can cause hardening of the arteries or atherosclerosis. This damage is usually caused by high blood pressure smoking or high cholesterol which leads to the formation of plaque on arterial walls. Plaque build-up is a progressive condition that often comes with no symptoms. Gradually it leads to blocked arteries that restrict the flow of blood.