This study was conducted on 106 mature white male rats. A complex of morphological methods of study was used in this scientific work. This dissertation presents a theoretical summary and a new solution of the scientific task to establish peculiarities of the structure and microvasculature of white rat’s myocardium under normal conditions and under the prolonged effect of an opioid, which will provide the opportunity to create the morphological basis for determination of the methods of prevention of the structural changes in the myocardium in case of the use of narcotic agents. After 7 days of daily nalbuphine injections electron microscopy showed edemas between the bundles of cardiomyocyte myofibrils, between the neighboring cardiomyocytes and platelet-erythrocytic sludges, nuclei of endotheliocytes with the signs of apoptosis in the microvessels’ lumens. After 14 days of the experiment there was found a partial separation of sarcolemma and myofibrils, marginal location of chromatin in the nucleus, invagination of the nuclear membrane; perivascular edema, presence of spreading masses of blood plasma in the vessels’ lumen, deformation of endotheliocyte luminal surface. After 28 days there were found areas of the destroyed sarcolemma, translucent nuclei of cardiomyocytes, destroyed mytochondria, Z-lines and M-lines, fragmented myofibrils, ruptured intercalated disks. On the 42-nd day of the experiment there was found expansion of the intercellular space caused by the swelling, mosaic damages of cardiomyocytes, where along with the preserved cardiomyocytes there are present destroyed sarcolemmas with villous deformation. Scanning electron microscopy of the white rat’s heart in the course of the experiment showed changes in the relief of the interior surfaces of the heart chambers: shortened microvilli at the initial stages of the experiment and their absence, laminiform formations at the later stages. Deposits of fibrin strings, various erythrocytic figures and cholesterol crystals have been found on the interior surfaces of the heart chambers. The entire interior surface of the heart chambers is covered with activated platelets and accumulations of altered erythrocytes (echinocytes, spherical, cupola-shaped, anular). Characteristic is the formation of erythrocytes and microthrombi sludges. After 7 days of the experiment the white rats of the experimental group showed a tendency towards the increase of the index of the ratio of mitochondria section area and the area of cardiomyocyte cytoplasm to 24.44 (19.75; 27.84) %, the control group showed 17.44 (12.16; 25.00) % with this index growing mainly owing to type 1 mitochondria. After 14 days of the experiment index of the ratio of mitochondria section area and the area of cardiomyocyte cytoplasm grew up to 26.74 (18.18; 31.87) % with greatest growth, compared with the control group, of type 3 mitochondria index. After 28 days of the experiment destruction of mitochondria had led to a drop of the indices of the ratio of mitochondria section area and the section area of cardiomyocyte cytoplasm to 19.48 (12.74; 28.7) %. Such a drop occurred mainly owing to the abrupt fall of the ratio of type 1 mitochondria. After 35 days indices of the ratio of the section area of type 1 and type 2 mitochondria and section area of cardiomyocyte cytoplasm fell to 12.5 (9.09; 15.58) % and 5.49 (2.34; 8.12) % respectively. Index of the ratio of type 3 mitochondria section area and section area of cardiomyocyte cytoplasm attained its maximum during the experiment and made up 5.68 (3.23; 12.79) %. Key words: myocardium, microvasculature, white rat, nalbuphine. Branch - Medicine.
