Intrauterine hypoxia (gestation days 15-19, pO 65 mm Hg, duration 4 h) led to an increase in the expression of p53, beclin-1, endothelial NO synthase (eNOS), and caspase-3 proteins in cardiomyocytes and reduced the number of mast cells in the heart of 60-day-old albino rats. Administration of a non-opiate analogue of leu-enkephalin (NALE peptide: Phe-D-Ala-Gly-Phe-Leu-Arg, 100 μg/kg) on days 2-6 of the neonatal period decreased the severity of delayed posthypoxic myocardial reaction. The content of eNOS cardiomyocytes and the total number of mast cells of these animals did not differ from the control parameters; the content of p53 cardiomyocytes was significantly lower than in animals exposed to intrauterine hypoxia. The cardioprotective activity of NALE was partially neutralized by co-administration with the NO synthase inhibitor (L-NAME, 50 mg/kg). Correction of the delayed posthypoxic changes, similar to the effects of NALE peptide, was observed after neonatal administration of its arginine-free analogue, G peptide (Phe-D-Ala-Gly-Phe-Leu-Gly; 100 μg/kg). Non-opiate analogues of leu-enkephalin NALE and G peptides can be considered as promising substances capable of preventing long-term cardiac consequences of intrauterine hypoxia.