Rhododendron brachycarpum has been known as a panacea in Korean folk medicine, and is used to treat various diseases including hypertension. Excessive ingestion can cause intoxication by grayanotoxin. We experienced a 59 year-old man suffering of grayanotoxin intoxication following excessive ingestion of Rhododendron brachycarpum. The patient presented dizziness, weakness, and chest discomfort with cold sweats. Electrocardiography showed marked sinus bradycardia with atrio-ventricular dissociation. With intravenous saline and atropine, the patient recovered. This case calls attention to the potential cardiotoxicity of Korean folk medicine Rhododendron brachycarpum.