Considering the significance of the unity distinguishing the level of aerobic energy generation in the myocardium, the morphological integrity of the mitochondrial membranes and the regulating influence exercised upon them by the hormones and mediators of the sympathoadrenal system the authors undertook a synchronous study of these factors in patients with rheumatic heart diseases when subjected to the cardiac valves prosthetics. These factors were found to play a key role in ensuring the contractility of the myocardium, this being confirmed by the results of clinico-biochemical comparisons. In a group of patients with dissociated processes of oxidative phosphorylation and a well-marked disintegration of membranous mitochondrial structures, as well as with a low adrenalin, noradrenaline and their precursors level in the myocardium, almost as a rule, in the early post-operative period there appeared symptoms of cardiac incompetence.