We report the case of a 42-year-old female, affected by mitral valve prolapse and ventricular arrhythmias, who died suddenly from ventricular fibrillation recorded during Holter monitoring. The lethal arrhythmia initiated with late diastolic couplets followed by a ventricular tachycardia that eventually degenerated into ventricular fibrillation. The patient had experienced four orthostatic and stress-related syncopal episodes, associated with nausea and diaphoresis, and a positive tilt test. Holter monitoring documented ventricular arrhythmias, consisting of both isolated monomorphic and sporadic repetitive beats. Her standard ECG and exercise test were normal, but signal-averaged study findings were significantly positive. QT prolongation in the absence of arrhythmias was observed during the Valsalva manoeuvre and isoproterenol infusion. 2D echo showed a remarkable mitral valve prolapse without regurgitation and localized structural abnormalities of the right ventricle. Postmortem study confirmed mitral valve prolapse, and also disclosed pulmonary infundibulum dilatation, massive adipose infiltration of the right ventricular free wall, patchy fibrosis and scattered myocardial inflammatory infiltrates in the left ventricle; these features are all consistent with arrhythmogenic right ventricular cardiomyopathy.