We report a case of severe bradycardia during general anesthesia due to reduced atrioventricular conduction capacity believed to have been caused by the trigeminocardiac reflex (TCR). A 46-year-old woman was scheduled for intraoral scar revision under general anesthesia. When the surgeon opened her mouth intraoperatively, the patient's blood pressure immediately increased, and she developed significant bradycardia and a transient Mobitz type II second-degree atrioventricular block. It was assumed that the mandibular division of the trigeminal nerve (V-3) was stimulated by the surgeon stretching the patient's mouth open while remifentanil simultaneously provided sympatholytic effects, resulting in activation of the TCR. The patient quickly responded well to atropine and had no additional complications.