We studied the parameters of mitochondrial respiration in the suspension of isolated heart mitochondria from old rats using glutamate and succinate – the substrates for the I and II respiratory chain complexes, as well as the dependence of this process on the action of calcium ions. It was shown that Ca2+ influx dynamics in old rat heart mitochondria is different from that in adult control organelles, and the maximum of fluorescence of the calcium-sensitive dye Fluo-4 AM at Ca2+ concentration 100 μmol/l was observed at 3rd minute and was 27% higher than in the control. Consequently, in older rats, we observed a more sharp increase in intramitochondrial calcium. Despite the moderate increase (using succinate) or no different from that in adult animals (using glutamate) of the V2 indicatorin the 24-month rats, ADP-stimulated respiration rate decreased, which led to a decrease in respiratory control ratio (RCR) by Chance and Lardy 1.18 and 1.6 times (with oxidation of succinate) and 1.18 and 1.4 times (in the presence of glutamate). However, the efficiency of phosphorylation of ATP, which is characterized by the ratio of ATP synthesis and oxygen absorption (ADP/O), did not change, nor did the velocity of phosphorylation of ATP (ADP/Δt). The effect of calcium ions on mitochondrial respiration in adult rats was dose dependent. At low concentrations of cation (10-7 mol/l), the Lardy’s RCR did not change, and Chance’s RCR and ADP/O ratio significantly increased, indicating an increase in the coupling of oxidation and phosphorylation processes. At the same time, in the old rat heart mitochondria, calcium ions, even at low concentrations (10-7 mol/l), did not significantly increase the rate of respiration and the ADP/O ratio. 10-5 and 10-4 mol/l Ca2+ resulted in a partial reduction of the activity of the respiratory chain in adult animals and significantly reduced the ADP-stimulated respiration, and the coefficients of RCR after Chance and Lardy in the elderly. +/Δt also tended to fall.