Structural reorganization of the myocardium was studied in rats of various age groups (periods of progressive and regressive growth) with anthracycline-induced regenerative and plastic insufficiency. The specific features included the prevalence of cardiomyocyte lysis, diffuse and microfocal changes, and diffuse or microfocal cardiosclerosis. During the late ontogeny, myocardial damage was characterized by more pronounced cardiosclerosis (primarily microfocal cardiosclerosis). The development of regenerative and plastic insufficiency of cardiomyocytes determines dilatation remodeling of the heart in rats of various age groups. Comparative study of the morphogenesis of heart failure in rats of various age groups showed that cardiotoxic exposure during the early ontogeny induced more pronounced remodeling of the heart compared to that in late ontogeny. Differences in proliferative activity of cardiomyocytes and ability for hypertrophic growth are the main cellular mechanisms of age-related features of structural reorganization.