We describe a case of profound bradyarrhythmia after sugammadex administration during ambulatory anesthesia. The patient was a 21-year-old man with autism spectrum disorder undergoing planned general anesthesia for dental treatment. After treatment completion, sugammadex was administered upon awakening, and sudden bradyarrhythmia appeared immediately. The patient’s heart rate decreased to approximately 30 beats/min but quickly recovered to roughly 80 beats/min after the administration of intravenous atropine. Electrocardiography suggested sinoatrial block or sinus arrest. Although the exact mechanism is unknown, severe electrocardiographic changes can occur within a few minutes of sugammadex administration.