The build-up that results is called plaque. Arteriosclerosis is a general term for the thickening and hardening of arteries. Some hardening of arteries normally occurs when people grow older. Plaque may partially or totally block the blood's flow through an artery. If either of these occurs and blocks the entire artery, a heart attack or stroke may result.
Atherosclerosis affects large and medium-sized arteries.
The type of artery and where the plaque develops varies with each person. Atherosclerosis is a slow, progressive disease that may start in childhood. In some people this disease progresses rapidly in their third decade. In others it doesn't become threatening until they're in their fifties or sixties. It's a complex process.