Ultrastructural changes in rat cardiomyocytes were studied after single administration of cyclophosphamide in the therapeutic dose. The major signs of cyclophosphamide-induced damage to cardiomyocytes included moderate lysis of myofibrils, dilation of vesicles in the granular and agranular sarcoplasmic reticulum, and destruction of mitochondria with the formation of myelin-like residual bodies. Ultrastructural changes in cardiomyocyte nuclei primarily manifested in variations of the shape, deep invaginations of the nuclear membrane, and translocation into the subsarcolemmal region.

Structural reorganization of the myocardium in response to antitumor agents (cyclophosphamide, betulonic acid and its amide) was studied. Cardiotoxic effects of these chemicals manifested in cardiomyocyte contracture and lytic injuries and by significant hemodynamic disorders. The most pronounced lytic and necrobiotic changes in cardiomyocytes were detected after injection of cyclophosphamide followed by betulonic amide; this led to a more pronounced decrease in heart weight as a result of a decrease in total cardiomyocyte count. Antitumor drugs differently changed the ratio of mono- to binuclear cardiomyocytes, which differ by their regeneratory and compensatory adaptive potential.