Objective: To estimate the microscopic, sub-microscopic and morphometric changes of the myocardium of the heart wall during early postnatal ontogenesis under the influence of pesticides which have passed through the mother’s milk. Materials and methods: The material for the experiment served as the slides of rat myocardium 205 different period of early postnatal ontogenesis. Results: Studies have shown that, when exposed manager that kinmiks thickness and atrial and ventricular walls at all ages is reduced as compared with the control group. The change depends on the type of pesticide, rat age and heart. Conclusion: When exposed to pesticides in the myocardium of the heart observed pathological changes indicative of developing toxic myocarditis.