Coloured computed tomography (CT) angiogram scans of the heads of a 57 year old male patient (left) and 59 year old male patient (right) showing the basilar arteries (centre of each scan). The right scan shows a healthy artery, the left scan shows a blocked artery causing an ischemic stroke or cerebrovascular accident (CVA). The basilar artery is at the back of the brain. The fronts of the heads are at right. An ischemic stroke is caused by a blockage or interruption of the blood supply to the brain. The lack of oxygen (hypoxia) damages the brain. Symptoms depend on the are affected. This blockage caused speech disturbances and weakness on one side of the body (hemiparesis).