Carotid artery disease happens when fat and cholesterol deposits (plaque) clog the carotid arteries on each side of the neck that deliver blood to the brain and head. Either a narrowing of the artery occurs, or when pieces of the plaque break off and lodge in a large artery, there is a blockage. This increases the risk of stroke because blood supply to the brain is reduced. There may be no symptoms, but if stroke symptoms like slurred speech and blurry vision occur, it should be treated as a medical emergency.