Purpose: Arterial anatomy that is insufficient for successful bypass grafting often leads to leg amputation in patients with severe ischemia. Flow-through free tissue transfer combined with lower extremity bypass provides vascularized soft tissue designed to act as a modulating AV fistula increasing blood flow through the bypass graft. Methods: 10 patients who otherwise would have undergone leg amputation were treated with arterial bypass and flow-through autologous free tissue transfer. RAFT Flap evaluation was performed using the ATL HDI 3000 Color Duplex ultrasound system using B-mode and Doppler spectra to determine graft patency, hemodynamics, and the presence and location of obstructive lesions. Results: Initial salvage rate in all lower extremity bypass + RAFT flap was 100 %. Arterial Doppler imaging detected elevated velocity at the RAFT flap in 4/10 patients. Elevated velocity (>200cm/s) was noted at the distal arterial anastomosis, compared to normal velocity of approximately 100 cm/s. Conclusion: In selected patients the RAFT flap with bypass appears to act as a self-modulating AV fistula, improving patency in situations where outflow may not support conventional bypass grafts. Postoperative monitoring of the RAFT flap with Color Flow Doppler offers non-invasive detection of increased flow velocities indicative of arterial and venous patency.