Keywords: Sus scrofa f. domestica; macroscopic structure; microscopic structure; myocardium; cardiomyocytes.

Abstract The cardiovascular system, which includes the heart, is one of the essential systems of the human and animal body. With its participation, the blood supply of the organs takes place; it promotes the outflow of lymph from the organs and its transport into the veins, and it helps to implement the functions of the organs of immune protection, endocrine, and nervous systems. The work aims to conduct a macro-, histo-, and cytomorphometric assessment of the morphological structures of the heart of the domestic pig using complex research methods (macroscopic, histological, morphometric). Functionally mature, clinically healthy animals (n = 7) of Sus scrofa f. domestica were used for the work. According to organometallic studies, the absolute weight of a pig's heart is 487.4 ± 8.12 g; the relative weight is 0.290 ± 0.004%, and the net weight of the heart is 461.4 ± 8.0 g. According to its linear dimensions, a domestic pig's heart is elongated-narrowed (conical) type, as evidenced by the heart development index of 155.1 ± 6.3%. According to the functional load of the muscle tissues of the myocardium of the heart and its separate morphological structures (ventricles and atria) when performing particular work during spontaneous rhythmic contractions, the absolute mass of the ventricles and atria is different. The enormous mass is characteristic of the left ventricle, then the right, and the smallest for the left and right atria. Therefore, the ventricles of the heart are more functionally developed, as evidenced by the ratio coefficient (1:0.79) of the mass of the ventricles to the net mass of the heart, respectively, the ratio coefficient (1:0.21) of the mass of the atria to the net mass of the heart and the ratio coefficient (1:0.27) atrial mass to ventricular mass. Cardiomyocytes of the left ventricle have the most significant volume, cardiomyocytes of the right ventricle have a smaller volume, and cardiomyocytes of the atria have the smallest volume. Their nuclear volumes have similar values, respectively, in the left ventricle – 77.16 ± 2.01 μm3, the right ventricle – 76.02 ± 2.43 μm3, and the atrium – 75.97 ± 3.24 μm3, and the nuclear-cytoplasmic ratio is different from them: the smallest nuclear-cytoplasmic ratio, respectively characteristic of cardiomyocytes of the left ventricle, significantly more for cardiomyocytes of the right ventricle and significantly the most for cardiomyocytes of the atria. The scientific results of morphoarchitectonics, organo-, histo-, and cytometry of the heart of the domestic pig presented in the publication supplement the information on the morphological structure of the heart of domestic animals in the relevant sections of histology, comparative anatomy and are a significant contribution to clinical cardiology.

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