Recent studies have suggested that a redistribution of cardiac output between splanchnic and nonsplanchnic vascular beds or changes in the venous resistance or venous compliance of one of these channels relative to the other would result in an intravascular redistribution of blood volume which would dramatically alter cardiac output and arterial blood pressure. The objective of this research is to re-evaluate systemic hemodynamics in the light of these findings. To accomplish this we will investigate the influence of adrenergic stimulation, alveolar hypoxia, and elevated left intraventricular pressure upon: (1) the distribution of cardiac output to splanchnic and nonsplanchnic vascular beds, (2) changes in venous resistance and venous compliance of these compartments and (3) the hepatic sphincter mechanism. In anesthetized dogs, a right heart bypass preparation will provide separation of venous return into: (1) blood draining the splanchnic bed and (2) blood draining the rest of the systemic circulation. Each channel will be drained by gravity into an extracorporeal reservoir. Total venous return will then be pumped to the pulmonary artery at constant flow. This preparation will allow the determination of the distribution of cardiac output to splanchnic and nonsplanchnic channels. Changes in venous resistance and compliance of these channels will be calculated from transient and steady state volume shifts which will occur following rapid drops in splanchnic, then peripheral venous pressures.