Currently, there are three prognostic indicators of ventricular electrical instability: long-term ambulatory ECG recording, programmed electrical stimulation and the signal-averaged electrocardiogram. Several clinical studies have suggested that frequent and complex ventricular premature contractions in patients with organic heart disease may identify future cardiac events, including sudden cardiac death although, with respect to prognosis, it is not likely that any grading system based on the ambulatory ECG will be without meaningful limitations. No study has adequately tested the hypothesis that decreasing ventricular arrhythmias after acute myocardial infarction reduces mortality. The inducibility of ventricular tachycardia during programmed electrical stimulation is regarded as an independent risk factor for sudden death. Predominantly due to the lack of standardized protocol and definitions, the actual relevance of current literature remains somewhat compromised. The indication for antiarrhythmic treatment in those patients in whom ventricular tachycardia can be induced has not been established with certainty since the effects of therapy on the prognosis are unknown. For patients with complex ventricular arrhythmias in whom sustained ventricular tachycardia cannot be induced, antiarrhythmic drug treatment does not appear indicated. Based on a number of studies, the presence of late potentials in the signal-averaged ECG has also been shown to be a meaningful prognostic indicator. The signal-averaged ECG, however, is not only subject to various technical problems but is also encumbered by limitations arising from electrophysiologic considerations. While no relationship could be established between late potentials and complex ventricular arrhythmias in the ambulatory ECG within the first two months after acute myocardial infarction, there was, however, a correlation between late potentials and the inducibility of ventricular tachycardia during programmed electrical stimulation. Consequently, the signal-averaged ECG may serve as a screening test to identify patients who should subsequently undergo programmed electrical stimulation for arrhythmia assessment or guided institution of treatment provided this proves to be effective in reducing the risk of future major arrhythmic events.