A stroke is a brain attack. It is a sudden interruption of continuous blood flow to the brain and a medical emergency. A stroke occurs when a blood vessel in the brain becomes blocked or narrowed, or when a blood vessel bursts and spills blood into the brain.

Some brain cells die because they stop getting the oxygen and nutrients needed to function. Other brain cells die because they are damaged by sudden bleeding in or around the brain. Some brain cells die quickly but many linger in a compromised or weakened state for several hours. Stroke causes permanent brain damage over minutes to hours.