The aim of the study was to assess the effect of mechanical right atrium distension of the isolated rat heart on the heart rate and heart rate variability, and the velocity of excitation wave propagation in the left ventricular myocardium using multielectrode mapping with flexible arrays. Materials and Methods. Experimental studies have been performed on the isolated rat heart in compliance with the Langendorff technique. Electrical heart activity was recorded using a flexible multielectrode array system. Results. Characteristic electrophysiological parameter changes of the isolated heart with the right atrium distension were detected using multielectrode mapping with flexible arrays. The flexible array design allowed registration of electrical potentials from the left ventricular surface of the actively contracting rat heart perfused according to the Langendorff technique and assessment of interconnection in the work of different parts of the heart: the right atrium in which the sinus node regulating the heart rate is located and the left ventricle. Application of multiple electrodes arranged in a specific way in the array made it possible to analyze spatio-temporal characteristics of electrical activity on the heart surface and to establish both the increase of the sinus node excitation frequency and excitation wave propagation velocity in the left ventricle. Conclusion. The growth of heart rate variability may suggest the existence of additional mechano-induced processes generating electrical instability in the distended atrium. The effects detected in the left ventricle with the given method may be caused by triggering intracardial regulation mechanisms.