The amplitude of delayed ventricular depolarizations, if detected from the body surface, is in the microV range. High amplification and signal averaging technique for improvement of the signal-to-noise ratio are necessary prerequisites to allow the registration of these signals. Delayed depolarizations are rather frequent findings in patients with coronary heart disease and marked left ventricular wall motion abnormalities. Additional spontaneous occurrence of ventricular tachyarrhythmias in these patients further increases the incidence of delayed depolarizations. They have also frequently been described in patients who suffer from malignant ventricular tachyarrhythmias or in whom programmed ventricular stimulation can provoke a repetitive response. Ongoing follow-up observation of altogether 1200 patients with coronary heart disease, who are involved in three prospective studies, suggest that delayed depolarizations have some prognostic significance to predict mortality from all cardiac causes and sudden death. But the predictive value of these potentials seems to be too low to draw definite conclusions or to indicate the need for specific therapy in the individual patient. The data published so far do not answer the question whether the results obtained from studies involving patients with coronary heart disease will have significance also for patients free from heart disease or for those with other than coronary heart disease.