Perinatal factors influence the course of the antenatal period of development, which ultimately affects an infant’s health and further development. Materials and methods. Experimental investigations were performed in 12 three-month-old female albino Wister rats weighing 180-200 g and their offspring (16 infant rats weighing 10-15 g). Throughout their pregnancy of 21 days, the female rats were intraperitoneally injected with sodium nitrite (NaNO2) at a daily dose of 5 mg/100 g body weight (the dose causing moderate hypoxia). Myocardial sections were stained by hematoxylin and eosin and by the hematoxillin basic fuchsin picric acid (HBFP) method to detect foci of acute ischemic and metabolic injuries. Material for ultramicroscopic studies was prepared using the standard methods. Ultrathin sections were examined under an electron microscope at an accelerating voltage of 125 kV. Immunohistochemical studies were performed using antibodies against α-smooth muscle actin (α-SMA) and desmin. Results. The basic morphological signs of hypoxic myocardial damage in newborn rats were presented as phenomena of mixed dystrophy, swelling, and destruction of contractile cardiomyocytes, myofibrillar lysis, and contractural changes. The characteristic morphological feature is mitochondrial ultrastructural damages in the contractile cardiomyocytes. At the same time, there were signs of perivascular swelling, capillary plethora, arteriolar emptiness and spasm, and endothelial cell damage. Conclusion. Antenatal hemic hypoxia induced by sodium nitrite has a pronounced pathological effect on the myocardium of newborn rats.