Structural and functional regularities of the course of adaptation and compensatory processes in organs and systems during surgical interventions on the abdominal and thoracic cavities under the influence of toxic endogenous and exogenous factors" (state registration number 0122U000031).Introduction.Today, cardiovascular disease is an important medical and social problem due to the fact that it is the most common, tends to grow, and often leads to disability and mortality in the population at a predominantly young working age [1,2,3]. Various ambiguous and contradictory statements in the biomedical literature regarding age-related cardiac remodelling exist. Some researchers argue that important criteria for adequate assessment of changes in parts of the heart muscle at the organ level are the determination of their spatial characteristics. It is known that in most cases, the expansion of the heart chambers is a sign of their damage [4,5].It should be noted that even modern diagnostic methods such as ultrasound, computed tomography, magnetic resonance imaging, and radiography do not provide all the data necessary to adequately determine the spatial characteristics of the heart parts and their changes with age and in pathology conditions [6]. Direct observation of the age-related spatial and pathological restructuring of the heart chambers in humans is impossible, so it is advisable to study these processes using induced experimental models, which allows for the complete analysis of these changes in the organ. During experimental studies, the role of modelling the pathological state, identifying the timing, causes and mechanisms of the formation of disorders in the heart chambers, their structural elements and components are increasing.The aim of the study.To determine the peculiarities of age-related changes in the planimetric and volumetric parameters of the heart parts of experimental animals using morphometric methods.Object and research methods.The study of planimetric and volumetric parameters of heart parts of 60 laboratory mature white male shrews, which were divided into two groups, was conducted. The first group consisted of 30 of these sixmonth-old experimental animals, and the second group consisted of 30 male laboratory rats aged 24 months. The animals were euthanised by bleeding under thiopental anaesthesia. In the study of the organs of experimental animals, no lesions of the cardiovascular, respiratory, endocrine, urinary, reproductive, or nervous systems were found. A thoracotomy was performed, and the heart was isolated from the thoracic cavity and cut into six parts according to a special technique [7]. The left and right ventricles, left and right atria, interventricular and atrial septa were isolated. Planimetry (measurement of the area) of the endocardial surface of the left (ESLV) and right (ESRV) ventricles, left (ESLA) and right (ESRA) atria was performed, planimetric (PI=ESLV/ ESRV) and atrial planimetric index (API=ESLA/ESRA), and inflow (IV), outflow (OV), and reserve (RV) volumes of the...