A 22-year-old woman presented with ventricular tachycardia and heart failure of acute onset, and rapid hemodynamic deterioration despite medical treatment. The heart failure required extracorporeal membrane oxygenation followed by cardiac transplantation. The histopathological mapping of the ventricular conduction system of the explanted heart revealed focal fibrosis of the myocardium in close proximity to the left posterior fascicle. There was no other evidence of myocardial infarction or myocarditis. Immunohistochemical staining did not demonstrate any cause of this lesion; however, atrophy of cardiac muscle fibers around the lesion was noted. The focal fibrosis was presumed to be the cause of the ventricular tachycardia.