The study deals with the interdisciplinary topic of the electromagnetic compatibility of the cardiac implantable electronic devices that are used in patients with a defect of heart conduction system. We are focusing on the detection of disturbing signals on electrodes of cardiostimulation device and its interpretation. The detection of electromagnetic interference (EMI) is related to electrode choice, device placement, its configuration and programming. The aim of the study is the analysis of the pacemaker response in the presence of an external source of the disturbance fields. We point to possible risks of its interaction and discuss mechanisms that can influence the pacemaker sensitivity to EMI. Due to improper signal detection, the device programming changes can occur. We present an experiment of the exposure of the cardiostimulation system to a low-frequency harmonic interference signals and finally we analyse similar clinical episode and discuss proper functioning of the pacemaker.