Femoral and jugular circulation times (NaCN method) were detd. before and after a femoral A-V fistula was made in 5 dogs, anesthetized with i.v. nembutal. Auricular pressures (after the method of Richards et al.) were likewise detd. Statistical analysis of results showed that an A-V fistula caused a significant reduction in the femoral circulation times from the site of the fistula to the heart, whereas the jugular circulation times showed no significant change. Following the introduction of a femoral A-V fistula, the auricular pressures increased significantly. This provides indirect evidence that an A-V fistula causes an increase in cardiac output.