A 42-year-old male was hospitalized in the surgical ward for abdominal pain due to stenosis of the splenic flexure of the colon and abscess around the stenosis. After segmental colectomy, the patient received intravenous continuous infusion of trimetaphan (Arfonad) to control his blood pressure. Twenty hours later, he developed bradycardia and hypotension followed by syncope. An electrocardiogram revealed marked prolongation of the QT interval and a prominent U wave associated with sinus bradycardia and/or sinus pause with junctional rhythm. Torsades de pointes type polymorphic ventricular tachycardia was the cause of the syncope, which appeared to be pause-dependent long QT syndrome caused by the ganglionic blocking action of trimetaphan in the presence of a hyperadrenergic state.