A burn of cardiac tissue at the distal pole of the pacemaker electrodes is described as one of the likely complications of electrosurgical interventions. However, the likelihood and clinical significance of this effect have not been sufficiently investigated. Aim. To study the thermal effect at the distal pole of the endocardial electrodes in order to ensure the safety of surgical interventions in patients with implanted heart pacemakers. Materials and methods. We have performed a clinical and experimental study of the thermal effect in tissues around the distal pole of the endocardial pacemaker electrodes in electrosurgical procedures. A mathematical modelling and experimental studies were performed in conjunction with study in cadavers. The outcomes of surgical treatment of 254 patients with implanted pacemakers were also assessed. Intraoperatively heart activity was controlled using a cardiac monitor. Detailed retrospective analysis of the heart activity during surgical interventions was carried out by means of the Holter monitoring in 28 patients. Results. In experimental surgical interventions thermal effect was identified in peri-electrode tissues. The heat intensity was dependent on the location of electrocoagulation electrodes in relation to the pacing system, power and duration of electrosurgical interventions. Mathematical modeling showed that the heart tissue damage was 2.7 mm in depth. The theoretical calculations were proved during experiments. The maximum thermal effect was achieved when lines of force of the electric field of electrocoagulation and the “distal pole-pacemaker body” axis were mutually directed. The safe location of the pacemaker electrodes was achieved when these axes were in mutually perpendicular planes and/or the pacemaker system out of the maximum tension of the pacemaker electric field. At the clinical stage reference electrode of electrocoagulator was placed in the safe position: during the abdominal and lower limb surgery it was placed under the right and left buttock and during the pacemaker zone surgery – in the left deltoideopectoral groove under the left shoulder. No significant thermal effect was found in most of the patients. A non-effective pacemaker stimulus was observed in 2 patients during the electrocoagulation. Conclusion. A thermal effect was observed during electrosurgical intervention in the tissue around the distal pole of the pacemaker endocardial electrodes that depends on the location of the pacing system in relation to the electrodes of electrocoagulator, power and duration of exposure. Clinical signs of the thermal effect were non-effective pacing, supraventricular and ventricular rhythm disturbances and primarily due to the violation of safety standards for electrosurgical procedures. The clinical significance of this effect is minimal when the suggested principles are adhered to and the pacing system is placed out of the lines of force of the electric field.