Anatomical and Histological Structure and Morphometric Features of the Heart of the Red Fox (Vulpes vulpes)

The heart is the central organ of the cardiovascular system, ensuring continuous blood circulation, the delivery of oxygen and nutrients to tissues, and the removal of metabolic waste products. Despite numerous studies describing the cardiac morphology of various animal species, the morphometric and histological characteristics of the heart of the red fox (Vulpes vulpes Linnaeus, 1758) remain insufficiently investigated. The aim of this study was to examine the anatomical, histological, and morphometric organization of the heart of sexually mature red foxes, including the determination of its linear dimensions, organometric parameters, ventricular and atrial morphometry, and the cytometric characteristics of cardiomyocytes. The study was conducted on clinically healthy sexually mature animals (n = 5) using anatomical, histological, morphometric, and statistical methods. Novel data were obtained on the macromorphological, histological, and cytomorphometric organization of the red fox heart. The heart was found to be ellipsoidal in shape and to belong to the broadened-shortened type. Its height was 6.52 ± 0.19 cm, width 4.42 ± 0.02 cm, circumference 11.8 ± 0.27 cm, and cardiac development index 147 ± 3.76%. The ventricles represented the most developed structural components, as confirmed by their morphometric parameters. The thickness of the left ventricular wall was significantly greater (P ≤ 0.001), exceeding that of the right ventricle by 3.23-fold, whereas the thickness of the left atrial wall exceeded that of the right atrium by 1.40-fold. The absolute heart weight was 40.6 ± 1.96 g, corresponding to 0.46 ± 0.015% of body weight, while the net heart weight without epicardial fat was 38.2 ± 1.85 g (0.43 ± 0.01% of body weight). The left ventricle accounted for the largest proportion of the net heart mass (52.1%), followed by the right ventricle (26.1%), whereas the atria together constituted 21.8%. The established ventricular-to-atrial mass ratios characterize the structural organization of the heart in this species. Histologically, the myocardium of both ventricles and atria consisted of cardiac striated muscle tissue formed by contractile cardiomyocytes arranged into myocardial fibers of varying thickness. These fibers were separated by layers of loose fibrous connective tissue containing blood and lymphatic vessels that provide trophic support and maintain myocardial functional activity. Cytometric analysis demonstrated that cardiomyocytes of the left ventricle were the largest. Their length was significantly greater than that of the right ventricle by 1.28-fold, while their width exceeded the corresponding value by 1.13-fold. The highest mean cardiomyocyte volume was also recorded in the left ventricular myocardium (7602 ± 78 μm³), compared with 4728 ± 114 μm³ in the right ventricle and 3425–3699 μm³ in the atria. Conversely, the nuclear-to-cytoplasmic ratio was lowest in left ventricular cardiomyocytes and highest in atrial cardiomyocytes, reflecting the functional specialization of different cardiac chambers. The findings substantially expand current knowledge of the morphofunctional organization of the red fox heart and may serve as reference data for comparative anatomy, cardiac morphology, veterinary morphology, clinical diagnostics, pathological anatomy, forensic veterinary medicine, and experimental studies of the cardiovascular system.