Stroke is a cardiovascular disease that affects the blood vessels supplying blood to the brain.   A stroke occurs when a blood vessel bringing oxygen and nutrients to the brain bursts or is clogged by a blood clot or some other particle. Because of this rupture or blockage, part of the brain doesn't get the blood flow it needs. Deprived of oxygen, nerve cells in the affected area of the brain can't function and die within minutes. And when nerve cells can't function, the part of the body controlled by these cells can't function either. The devastating effects of stroke are often permanent because dead brain cells aren't replaced.

There are four main types of stroke: two caused by blood clots or other particles, and two by bleeding or hemorrhage . Cerebral thrombosis and cerebral embolism are by far the most common, accounting for about 70-80 percent of all strokes. They're caused by clots or particles that plug an artery. Cerebral and subarachnoid hemorrhages are caused by ruptured blood vessels. They have a much higher fatality rate than strokes caused by clots.