Nearly 700,000 people in the United States experience a stroke each year, 200,000 of which are repeat strokes. A stroke occurs when the blood flow to your brain is interrupted. Your brain gets most of its blood supply through large arteries on each side of the neck called carotid arteries. The most common cause of a stroke is the accumulation of plaque in your carotid arteries, which narrows and blocks blood flow through the arteries. When enough plaque has built up in the carotid arteries to interfere with the flow of blood to the brain, a person is said to have carotid artery disease.