We describe an autopsy case of fatal poisoning due to accidental overdose of pilsicainide, which is a Vaughan Williams class IC antiarrhythmic drug (a pure sodium channel blocker). A man in his 50s was found dead in his home at approximately noon. He had ischemic heart disease and insomnia, and had previously demonstrated improper prescription drug adherence. The autopsy revealed old coronary artery bypass grafting and mild fibrosis of myocardium, but no acute myocardial infarction was found in microscopic examination. Toxicological analysis also identified a high blood concentration of pilsicainide (femoral vein blood, 14.9 μg/mL), more than 15 times higher than reported therapeutic levels. The blood concentrations of other drugs were at therapeutic levels, and no alcohol was detected. We concluded that the cause of death was pilsicainide poisoning, based on the results of the autopsy and the toxicological examination. This is the first autopsy report of fatal poisoning due to pilsicainide as a single agent.