In the absence of autopsy studies, the etiological diagnosis of this form of ventricular fibrillation (VF) depends on the exclusion of cardiac disease by all available invasive and non-invasive diagnostic methods. Primary VF is rare and affects young adults. There are few clinical markers and published electrophysiological data indicates that sustained ventricular tachycardia or VF is unlikely to be induced by programmed ventricular stimulation. The underlying mechanism of the arrhythmia is poorly understood. However, a possible arrhythmogenic substrate has been suggested in small zones of fibrosis within normal Purkinje tissues, as encountered in some minor forms of arrhythmogenic right ventricular dysplasia. Also, the role played by the autonomic nervous system in triggering VF seems to be particularly important. Some described cases resemble curiously "torsades de pointes" with a short coupling interval. The "cardiac" prognosis of resuscitated patients is usually good. However, arrhythmic recurrences are common, and, classically, antiarrhythmic drugs are usually ineffective. The indication for implantation of an automatic defibrillator is therefore justified in patients surviving primary VF. The lack of understanding of this condition is an argument in favour of setting up a French register of patients with primary VF in order to establish its clinical features.