Temporary endocardial decelerating stimulation of the heart was conducted 151 times in 57 patients with various tachysystolic disorders of the rhythm. The values of central and intracardiac hemodynamics were studied in some patients against the background of decelerating stimulation. Definite groups of patients were distinguished according to the results of decelerating stimulation. In 17 patients decelerating stimulation of the heart served as an independent method of treatment of cardiac arrhythmias the underlying factor of which was the re-entry mechanism. In 11 patients paired and combined stimulation of the ventricles promoted the normalization of the values of hemodynamics and myocardial metabolism which had occurred against the background of severe disorders of the rhythm. In 14 patients with marked electric instability of the myocardium due to various causes, decelerating stimulation allowed time to be gained for choosing and carrying out adequate drug therapy.