Left-sided vertebral artery stenosis, if it occurs slowly, is usually not life-threatening and may not even have any noticeable symptoms. However, if the stenosis occurs suddenly, it may induce severe brainstem infarction, which is life-threatening. Most stenosis of the left vertebral artery is caused by atherosclerotic plaque that gradually increases in size and blocks the lumen. It affects the blood supply to the brain, especially to the brainstem and cerebellum, leading to manifestations such as dizziness and lightheadedness. This condition is usually not life-threatening. However, in the case of a sudden onset of left-sided vertebral artery stenosis, such as a cardiogenic embolus dislodged into the vertebral artery, or rupture of plaque, thrombosis of the vertebral artery itself, or a significant reduction in blood volume leading to hypoperfusion. Because the arteries and brain tissue downstream of the vertebral artery are too late to compensate, acute cerebral infarction may occur, which is life threatening. If a patient is found to have left-sided vertebral artery stenosis, he or she needs to go to the hospital in a timely manner, so that the doctor can decide on the next step of treatment according to the patient’s specific situation and prevent life-threatening injuries.