Abstract <p>The issue of cardiovascular regulation during aging receivesinsufficient attention despite its high social significance. Thecommon pathogenesis of cardiovascular regulation disorders in experimentalanimals and elderly individuals makes it relevant to study the mechanismsof myocardial contractility regulation in comparative experimentson laboratory animals of different ages. To identify the specificchanges in length-dependent mechanisms regulating the contractilityof healthy myocardium during aging, the characteristics of mechanicaland electrical activity, as well as the kinetics of intracellularcalcium ion concentration (calcium transient, CaT), were assessedin single contractions of the right ventricular myocardium in groupsof young (1 month) and old (2.5 years) rats. The experiments werecarried out on the right ventricular trabeculae of the male Wistarrat hearts. The indices of mechanical tension, CaT, and action potentials(APs) were recorded in an isometric contraction mode under varyingdegrees of stretching. It was found that the myocardium of old animalsis characterized by a lower amplitude of isometric tension, a reducedrate of isometric tension development, and a longer AP durationcompared to young animals. For the first time, age-related featuresof length-dependent changes were detected upon superposition ofCaT curves obtained at different preloads of the ventricular myocardium.In old rats, the CaT decay time at 30% of the amplitude was significantlylonger than in young animals. Our original method of CaT differencecurves revealed the influence of preload on calcium ion kineticsin cardiomyocytes of multicellular ventricular myocardial stripsin rats of different ages. Specifically, the relative amplitudeand area of segment III of the CaT difference curves were significantlygreater in young animals compared to old ones.</p>