The objective of this work is to induce sustained chronic (3 months) elevation of the cardiac output in dogs. Left stellate ganglion stimulation and cardiac pacing will be employed in instrumented, unanesthetized Greyhound and mongrel dogs. The aim is to provide a model for study of the circulatory response to an increased cardiac output not brought about by elevating tissue metabolic activity. This experimental preparation will allow investigation of evidence indicating that inappropriately elevated cardiac output in itself may contribute to hypertension in man and experimental animals; that high blood flow increases susceptibility to atherosclerosis; and that increased cardiac output results in vascular changes which cause elevated peripheral resistance.