[Mechanical action of the atria during stimulation on the work of the sinus node]

The cardiac pacemaker and atria were removed from the frog heart and placed into a chamber with Ringer solution. Atrial pacing was performed at a suprathreshold milliamperage. The mechanism of changes in the cardiac pacemaker during atrial pacing was studied both under the conditions of the blockade of the intracardiac nervous system and elimination of the bioelectrical and mechanical effects of the atria on the cardiac pacemaker. It is inferred that the change in the rate of pacemaker stimulation during atrial pacing is largely determined by the mechanical activity of the atria.