We performed morphological assay of the myocardium in Wistar rats with anthracycline cardiomyopathy and SHR rats with genetically determined arterial hypertension causing hypertrophic cardiomyopathy. Both disorders were accompanied by a decrease in protein synthesis and development of plastic cardiomyocyte insufficiency. Electron microscopy revealed peculiarities of intracellular regeneration of cardiomyocytes. We observed disorientation of newly formed myofibrils lying between preserved myofibrils. These myofibrils were positioned perpendicular or at angle to the long axis of muscle fibers, or extended from the Z line (in a fan-like manner) crossing each other. Regeneration disturbances also included excessive elongation of myofibrils. These abnormalities of myofibril regeneration were related to changes in transcription and translation in cardiomyocytes, due to DNA damages caused by cardiotoxic doses of rubomycin.