The condition of blood vessels that have thickened, hardened, and lost their elasticity-"hardening of the arteries." Aging and the formation of blood-derived fatty plaques within or directly beneath the inner lining of the arteries are the common causes. Many of the large arteries aid blood transport from the heart by their rebound elasticity, "kicking" it out; smaller ones have muscle coats that need to contract and relax in response to nerves. All this is compromised when there is arteriosclerosis.