Despite advances in cardiovascular medicine, the endogenous mechanisms responsible for positive inotropic state of the heart is poorly understood. We have assessed surgical transposition of the portal vein (portacaval shunt) as a procedure providing total systemic delivery of portal venous effluent in six dogs. The animals recovered rapidly from the surgery maintaining euglycemia. Four days after surgery the serum enzymes such as alkaline phosphatase, alanine aminotransferase and gamma glutamyl transferase returned to normal values, whereas all the animals had significantly higher values of urine volume and left ventricular dP/dt. Pre and postoperative left ventricular pressure was unchanged. Our results indicate that portacaval shunt plays an endogenous role in the positive inotropic state of the heart, and suggest that this surgical procedure may provide an insight into its beneficial role in heart failure.