Modern pacemakers and implantable defibrillators provide a multitude of technical algorithms and parameters, which can be programmed individually and can treat different forms of arrhythmias. Stored electrograms offer the possibility to obtain valuable information during follow-up (but also in real-time) about arrhythmias and device function or malfunction. This results in improved treatment of cardiac arrhythmias and heart disease. Due to constant innovation and development of these systems, it requires, however, profound biomedical and technical knowledge, since stored electrograms may display complex arrhythmias and device reactions that are not easy to interpret. Understanding of stored device information improves follow-up and facilitates individual care for the patient.