Increased flow velocity in the left middle cerebral artery indicates stenosis or spasm of the left middle cerebral artery. Increased flow velocity in the left middle cerebral artery is what transcranial Doppler describes for examining the target vessel. Focal increases in blood flow velocity occur as blood passes through more narrowed areas. Common causes include atherosclerotic plaque formation, congenital stenosis, inflammatory changes in the vessel, and cerebral vasospasm. Cerebral angiography can be performed to determine the location and degree of stenosis. Stenosis caused by atherosclerotic plaque formation is usually treated with oral medication and, if necessary, interventional surgery. In patients with increased blood flow in the middle cerebral artery due to vasospasm, the increased flow velocity in the middle cerebral artery will be relieved after oral treatment with anti-cerebral vasospasm medication and a repeat transcranial Doppler examination. If the phenomenon of increased flow velocity in the middle cerebral artery occurs, one should consult a doctor in time to clarify the cause of the disease so that the next step of treatment can be carried out.