We describe a case of a three year old unvaccinated child who developed a fulminant diphtheric myocarditis and nephritis four days after the onset of a tonsillar diphtheria. Despite of the administration of antitoxin on day three and four the child died within 48 hours from the beginning of rhythm disturbances. The cardiac involvement rapidly progressed from bradyarrhythmias with the necessity of a temporary pacemaker to ventricular rhythm disturbances with cardiac failure and final ventricular fibrillation.