[Analysis of depression of contractions of the isolated dog heart following paired stimulation].

In 30 experiments in isolated canine hearts perfused with whole donor blood disorders in myocardial contractions were studied following the termination of paired stimulation. It was concluded that the cause of depression of cardiac contractions following paired stimulation is not myocardial hypoxia and energy reserve exhaustion during enhanced mechanical activity of the heart, but a dissociation of the electric and mechanical processes in the myocardium; switching off the second (stand-by) action potential together with the termination of the paired stimulation caused disorders in the regimen of coupling processes that have established themselves under this form of electric stimulation. This suggestion is supported by the fact that repeated paired stimulation during depression is capable of producing the same stimulating effect upon the cardiac contractions as the initial one. The depression was eliminated by the administration of potassium ions and catecholamines.