The Holter function of implanted devices will record events with characteristics meeting criteria determined by the manufacturer or programmed by the physician. It does not show a continuous ECG. It is reliable, provided the basic functions of the device are operating correctly. This is an ideal tool for assessing the electrophysiologic profile of heart disease patients with implants and to assess the efficacy of various treatments (anti-arrhythmic drugs, ablation procedures). Combined with telemedicine technology, it can provide early alerts to the physician about deterioration in the rhythmic or hemodynamic status of their patients and thus prevent complications that would otherwise have led to costly hospitalizations. It is a very reliable tool to assess ICD function (diagnostic capabilities by the discrimination algorithms and efficacy of the delivered therapies). The technology will evolve and offer extended data in the future, such as sensor information or repolarization data (ST segment, QT duration, variability, &c.).