Coloured computed tomography (CT) angiogram scan of the head of a 59 year old male patient showing a blocked basilar artery (centre) causing an ischemic stroke or cerebrovascular accident (CVA). The basilar artery is at the back of the brain. 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).