Reflex regulation of the cardiovascular system is dependent upon the detection of pressure, volume, or chemical changes by receptors located within the cardiovascular system and within the lungs. A number of receptor sites have been located within major thoracic arteries and vein, in the pulmonary blood vessels, and within the various chambers of the heart. The reflexes initiated by stimulation of these receptors interact with sinoaortic baroreflexes to regulate cardiac function as well as regional vascular resistances in various vascular beds. The proposed investigation seek to determine if cardiopulmonary receptors may regulate cardiac function and peripheral vascular resistance by directly interacting with spinal cord and sympathetic ganglion components of neural control, in addition to more central neural regulatory mechanisms. Initial studies indicate that a short loop feedback mechanism exists in thoracic sympathetic ganglia and that this mechanism of regulation may be initiated by cardiopulmonary receptors.