Primary ventricular fibrillation especially occurs during the first hours after acute myocardial infarction and is often not preceded by premonitory ventricular premature beats. In hospital primary ventricular fibrillation can be prevented by an intravenous lidocaine regimen in a rather high dosage. By contrast the effectiveness of intramuscular lidocaine in preventing out-hospital primary ventricular fibrillation is unestablished. If recurrent attacks of primary ventricular fibrillation supervene, intervention with antiarrhythmic therapy and/or cardiac pacing is often unsuccessful. Repeated defibrillation should be carried out under these circumstances. If properly treated primary ventricular fibrillation is associated with a good short and long term prognosis.