Every minute one patient in the world suddenly dies, of heart disease in the vast majority of the cases. Most of these sudden deaths of cardiac origin are due to ventricular tachycardia and/or fibrillation on a background of ischaemic heart disease. It is now recognized that as much as left ventricular dysfunction these ventricular arrhythmias are of sombre prognosis. To prevent sudden death of cardiac origin, therefore, patients with severe ventricular arrhythmia and consequently at high risk must be identified. Among examinations used for this purpose, the Holter monitoring method is of considerable value as it provides qualitative and, mostly, quantitative information on the arrhythmia. Programmed stimulation--a much more invasive method--has a prognostic value which varies from one author to another. On the other hand, late potentials recording is a simple and innocuous procedure, apparently most reliable as indicator of complex ventricular arrhythmias and sudden death. In spite of all these recent technical advances, the prevention of cardiac sudden death remains problematic since no epidemiological study has yet demonstrated that major reduction or even suppression of ventricular arrhythmias by antiarrhythmic drugs can significantly reduce the coronary mortality rate.