Stroke most often occurs when blood flow to the brain stops because it is blocked by a blood clot. When a blood clot blocks the blood supply to the brain, parts of the brain may not get enough blood and oxygen to survive. As a result, permanent brain damage can occur, which can affect a person's ability to walk, talk, and function independently. In order to reduce the risk of permanent damage, it is important to restore blood flow to the brain as quickly as possible.