[A new model of the cardio-cardiac reflex]

A special cardiac vagal afferent stimulation was used in frogs. Bursts of stimuli were applied to the central end of the left cardiac bransh of the vagus with frequency of 1 burst per a heart beat during 2--5 heart beats. In this way the R-wave of the ECG triggered the stimulator after a desired delay. The stimulation induced hypotension and decreased the heart rate, both effects being abolished by cutting the right cardiac branch of the vagus. Every burst of stimuli applied to the left cardiac branch evoked a discharge of the efferent cardiac fibers in the right vagus. Both bradycardia and the energy of the efferent discharges were found to depend on the intensity of stimulation and on the bursts relation to the phases of the cardiac cycle. Maximal cardiac slowing and maximal energy of the efferent vagal discharges were observed when the bursts were synchronized with S--T interval, while minimal those - when the stimulation occurred during T--P interval of the ECG.