Electromagnetic interference and compatibility are problems that claim an increasing attention of biomedical industries, all over the world. For electromagnetic interference we intend a phenomenon that can occur when an electronic device undergoes the influence of an electromagnetic field, which may cause temporary or definitive malfunctioning of the device itself. Indeed, electromagnetic compatibility is the capacity of an electric device either to operate normally, without generating electromagnetic disturbances that may interfere with other devices or to operate without being influenced by electromagnetic field generated by other electric devices. Pacemaker (PM) and implantable-cardioverter defibrillator (ICD) functioning can be significantly compromised by electromagnetic fields, even though their circuits, nowadays, are well protected from most of electromagnetic wave sources. The basis for electromagnetic interference on PM and ICD lays on different factors even physical such as the power of external signal, the distance between the signal and the PM and ICD, the frequency range, modulation type and immunity level of the PM and ICD. The electromagnetic interference on PM and ICD may result into a temporary or permanent malfunctioning, like pacing inhibition, asynchronous pacing, or the switching of the pacing mode. The purpose of this work is to give useful indications for a correct in-hospital management of patients with PM or ICD, in order to avoid dangerous electromagnetic interference.