Episodes of transient ISCHAEMIA of some part of the cerebral hemispheres or the brain stem (see BRAIN) lasting anything from a few minutes to several hours and followed by complete recovery. By definition, the ischaemic episode must be less than 24 hours. These episodes may be isolated or they may occur several times in a day. The cause is ATHEROMA of the carotid or vertebral arteries (see ARTERIES, DISEASES OF) and the embolisation (see EMBOLISM) of PLATELETS or CHOLESTEROL. These attacks present with signs suggesting a stroke (see STROKE) but which rapidly resolve.