The effect of distending a pouch of the left atrium on the heart rate.

1. A pouch has been prepared consisting of a part of the wall of the left atrium together with the left pulmonary vein-atrial junctions.2. An increase of perfusion pressure in the pouch caused a reflex increase in heart rate.3. The afferent path of the reflex was in the vagus nerves and the efferent path was in the sympathetic nerves.4. The receptors most likely to be stimulated by an increase in pressure in the pouch are those receptors situated in the subendocardium of the pulmonary vein-left atrial junctions.