A sudden interruption of blood flow to a portion of the brain causing injury. Some strokes are associated with bleeding into the damaged area. Most strokes are caused by a blocked artery in the brain from hardening of the arteries (atherosclerosis) or from a blood clot that travels from another area (embolus). The symptoms experienced depend on the artery blocked. Survival and the best outcome depend on seeking medical care immediately. Also known as a stroke.