block off a blood vessel and cause a stroke well most of the causes are summarized here the number one cause is atherosclerosis also known as hardening of the arteries so it's the same process that causes a heart attack it builds up cholesterol plaque and the blood vessels of the heart and that's going to cause a lack of blood flow and a lack of oxygen to the heart if it does it on the way to the brain it's going to cause a stroke so this is the aortic arch that comes off the heart this can develop atherosclerosis here's the carotid