Almost 50 percent of patients with chronic heart failure die of sudden death often due to arrhythmia. In these patients the prognosis is related to the severity of myocardial lesions and also, probably, to the presence of ventricular arrhythmias. The potential severity of which can be assessed by various methods, including ECG, Holter monitoring, late potentials study and programmed ventricular stimulation tests. The first therapeutic measure to improve the prognosis of heart failure is to improve the myocardial function by prescribing converting enzyme inhibitors. The second measure consists of acting on potentially dangerous ventricular arrhythmias with few or no symptoms. Among antiarrhythmic agents, only beta-blockers and amiodarone seem to be valuable.