Carotid artery stenosis is a narrowing of one or both of the carotid arteries. These blood vessels supply blood to your brain. They can be narrowed and damaged by the buildup of fatty deposits called plaque (say "plak"). This plaque may limit blood flow to the brain. If this plaque breaks open, it may form a blood clot. Or pieces of the plaque may break off. A piece of plaque or a blood clot could move to the brain and cause a stroke or transient ischemic attack (TIA).