Accurate and correct description of morphological changes in the myocardium in experimental animals is of great importance for understanding the pathogenesis, the mechanism of the relationship between changes in structure and function. The heart is located in the thoracic cavity and is almost completely surrounded by the lungs and is free only in the anterior-inferior region. Heart rate and rhythm are regulated by the autonomic and endocrine systems, hemodynamic factors [15]. Blood supply to the heart is carried out by the left and right coronary arteries; they do not have numerous collaterals. The left coronary artery passes in the groove between the left atrium and the pulmonary artery, intramyocardially. Rats do not have a true circumflex artery of the heart [3].