The effect of stretching the superior vena caval-right atrial junction on right atrial receptors in the dog.

1. Action potentials were recorded from fibres in the right cervical vagus, the receptor endings of which were localized to the endocardial surface of the superior vena caval-right atrial junction.2. Stretching the junction between the superior vena cava and the right atrium without obstructing venous return caused an increase in the discharge of these fibres. This increase in impulse frequency was similar to that caused by small changes in mean right atrial pressure (range 0-13.5 cm H(2)O).3. This evidence supports the earlier suggestion that stimulation of the right atrial receptors by stretching the superior vena caval-right atrial junction causes a reflex increase in heart rate.