Proceedings of the International scientific and practical conference ―Science, technology and culture: integration and prospects‖ (November 3-5, 2025) / Publisher website: www.naukainfo.com. – Kharkiv, Ukraine, 2025. - 254 p.

84 solution of glutaraldehyde with subsequent post-fixation in a 1% buffered solution of osmium tetroxide. The samples were dehydrated and embedded in Epon-812 epoxy resin. Ultrathin sections were examined using a transmission electron microscope ПЭМ-100-01 ("SELMI", Ukraine). Research results and their discussion. The results of electron microscopy showed ultrastructural changes in the microcirculatory bed of the heart ventricles. The general architecture and integrity of the blood microvessel wall on the 1st day of postnatal development were not disturbed, but signs of dystrophic changes in the endothelium of hemocapillaries and the development of perivascular edema were found. Perivascular edema is characteristic of hemocapillaries, but is absent near the microvessels of the afferent and drainage links of the microcirculatory bed. Cytopathological changes in contractile cardiomyocytes consisted of cytoplasmic swelling, mitochondrial swelling and fragmentation, and disorganization of individual myofibrils. Newly formed micromitochondria with single cristae were found mainly near the nucleus, interfibrillar mitochondria with signs of crystallolysis. On the 7th day of the experiment, ultrastructural signs of progressive dystrophic changes were detected: an increase in the relative density of micromitochondria, pronounced lysis and disorientation of myofibrils, and the appearance of cardiomyocytes in a state of apoptosis. Conclusion. Based on the results of the assessment of ultrastructural changes in the myocardium, a conclusion was made about the cardiotoxic effect of lead acetate, which consists in damage to the endothelium of blood vessels and direct and/or indirect induction of degenerative changes in cardiomyocytes. The cardiotoxic effect caused destructive changes at the level of contractile myofibrils and edema and fragmentation of mitochondria, which indicates a violation of the energy supply of cells and a violation of their contractile function.