Over the last decades, the number of patients with cardiac stimulation devices (including pacemakers, resynchronization devices and automatic implantable cardiac defibrillators) has increased exponentially, exposing an ever increasing number of health professionals from different areas of medicine to their electrocardiograms. Thorough knowledge of proper device function is crucial to understanding electrocardiographic changes induced by cardiac stimulation, identifying normal findings, and recognizing the different manifestations of device malfunction. In this article, basic concepts on device design, programming and proper function will be discussed, allowing the reader to develop an organized step wise approach to interpret the electrocardiogram of patients with cardiac stimulation devices.