1. Localized distension of the junction between the superior vena cava and the right atrium without obstructing venous return caused an increase in heart rate.
2. This increase in heart rate was a reflex response; the afferent path was in the vagi and the efferent solely in the sympathetic nerves.
3. The receptors most likely to be stimulated by the distension of the junction between the superior vena cava and the right atrium are the right atrial receptors located on the endocardial surface of the intrapericardial portion of the superior vena caval—right atrial junction.