Stroke refers to a brain injury that is caused by an inadequate supply of blood (ischemia) to the brain. Transient ischemic attacks (TIAs) are temporary episodes that resemble a stroke. They are regarded as serious warning signs that a stroke may occur in the future.Because the brain is the organ affected by strokes, if you have a stroke you will be attended to by a neurologist. However, strokes are closely related to cardiovascular disease and therefore are mentioned here.Causes of Stroke. Many strokes a caused by a small bit of clot or cholesterol debris breaking off from its site formation in the carotid arteries in the neck. The clot travels up in the bloodstream through smaller branches of tl artery until it becomes wedged into, small branch in the brain and blocks further blood flow. This is called a cerebral embolism.Clot or debris can also form in the aorta upstream from the branches of the carotid arteries or in the left side of the heart such as the left atrium, left ventricle, and artificial valves in the aortic or mitral position. The clot can break off and travel to the brain, when it causes a stroke.Atherosclerosis or a blood clot that forms and stays in the carotid or cerebral artery (arteries in the neck and brain) can block blood flow enough to cause TIAs or a stroke. This condition, called cerebral thrombosis, differs from cerebral embolism in that the clot has not moved from its site of origin.A less common but important cause of stroke is formation and release of a blood clot from a vein in the legs (an event that in itself is not rare) that travels to me heart. The clot crosses from the right side of the heart to the left side of the heart through an abnormal opening in the septum (partition that divides the atria and ventricles). From the left side of the heart, the clot then proceeds through the arterial circulation into the brain, where it causes a stroke. This event is occasionally the first sign that there is a hole in the wall separating the two sides of the heart (septal defect).Not all strokes are caused by clots or obstruction. Other causes of stroke include bleeding into the brain (cerebral hemorrhage) or around the surface of the brain.*195\252\8*