A system for creating an arteriovenous (AV) fistula comprises a vessel access sheath having a hollow interior and an exit port, a side access needle catheter configured to fit within the hollow interior of the sheath, a needle configured to be inserted into a blood vessel through the side access needle catheter, a toggle delivery catheter configured to fit within the hollow interior of the sheath, and a toggle apparatus configured to be delivered into a vessel through the toggle delivery catheter. The toggle apparatus comprises a shaft and a toggle member pivotably attached to a distal end of the shaft. A source of RF energy or resistive heat energy may be provided for application to the toggle member and/or to a heater insert in the toggle delivery catheter, for the purpose of creating the fistula.