The authors analyzed the antioxidant activity of reamberin and cytoflavin and evaluated their cardioprotective effect, by investigating lipid peroxidation and oxidative modification of plasma proteins, as well as the ultrastructure of newborn rat cardiomyocytes under chronic hemic hypoxia induced by sodium nitrite. Reamberin and cytoflavin can reduce the manifestations of mitochondrial dysfunction and the degree of cardiomyocyte damage in the neonatal rats due to the antioxidant and membrane-protective properties of the drugs. Succinic acid in combination with the metabolic components of the drugs significantly inhibits lipid peroxidation, by improving the structure of membranes and the mitochondrial function of cardiomyocytes.