Left-sided cerebral infarction, clinically, refers to infarction of the left cerebral hemisphere. When the disease involves the left cortical brainstem bundle, tongue extension is deviated to the opposite side of the lesion, that is, tongue extension is deviated to the right side. Similarly, in the case of damage to the internal capsule of the left cerebral hemisphere, hemiparesis, hemianesthesia and hemianopsia can occur on the opposite side of the lesion, that is, on the right side, which is the triple hemianopia syndrome. Clinically, it is common for patients with infarction of the left cerebral hemisphere to present with left-sided corner of the mouth, shallow right nasolabial fold, right-sided tongue extension, right-sided limb paresis, and right-sided hemianesthesia. When similar symptoms occur, patients should be alert to cerebrovascular disease and promptly go to a hospital with a stroke unit and be seen in the neurology, neurosurgery or emergency department.