[Effect of adaptation to physical load on the efficiency of oxygen utilization by the heart]

The mechanical performance, oxygen consumption, and external efficiency of isolated working hearts taken from control and trained rats were studied. Elevation of calcium concentration in perfusate from 1.25 to 2.5 mm and increase in external work were noted in the hearts of both the groups. This increase in the trained hearts was two-and-a-half times of that in the control rat hearts, while oxygen consumption was equally elevated in both the groups. As a result the efficiency of oxygen utilization by the heart for external work was higher in the trained hearts than in the controls. The results obtained may be explained by the greater functional power of the calcium transport system in the myocardial cells of trained animals.