Introduction: Among chronic diseases of the cardio-vascular system, arterial hypertension of heterogeneous etiology leading to myocardial hypertrophy is the most common. Methods: The sequence of depolarization and architecture of the myocardial left ventricle (LV) and interventricular septum (IVS) of normotensive Wistar rats (n = 30), Wistar rats with experimentally induced renovascular hypertension (n = 15, the Goldblatt model), and ISIAH rats with inherited stress-induced arterial hypertension (n = 7), were studied. Results: In ISIAH rats, an even increase in thickness of the walls of the LV and IVS was revealed. The significant change of orientation of all myocardial layers did not occur due to the thickening of fibres of the circular layer. In rats with renovascular hypertension, the heterogeneous thickening of the walls of the LV and IVS, thickening of the subendocardial layer, the fibres of which are longitudinally oriented, and the change of thickness and orientation of the circular layer were revealed. In animals with myocardial hypertrophy of different genesis, the excitation wave in the ventricles spreads successively from the endocardium to epicardium as in the case of normotensive Wistar rats. In hypertensive animals, in the areas of most thickening of the circular layer, the excitation wave spreads unevenly with delays. Conclusion: The increase of ventricular depolarization duration in animals with hypertrophy of different genesis is connected with hypertrophy of myocardial fibres and an increase of connective tissue volume compared to normotensive animals.