Ventricular late potentials are due to regionally depressed inhomogenous conduction, mainly in the border zone of a previous myocardial infarction. They can be recorded noninvasively using high-resolution signal-averaging techniques. They are almost never detectable in normals, whereas they represent a frequent finding in postmyocardial infarction patients. The presence of ventricular late potentials after previous myocardial infarction predicts the subsequent occurrence of hemodynamically severe sustained ventricular tachycardia and/or sudden cardiac death. Their predictive significance can be increased by combining signal-averaging with long-term ECG recording and estimates of left-ventricular ejection fraction. However, despite recent major improvements in identification of patients at risk, there is still a need for an effective mode of prevention of serious ventricular tachyarrhythmias after myocardial infarction.