BACKGROUND: Venous congestion is a leading cause for free flap failure and still relies on clinical observation as the diagnostic gold standard. We sought to characterize blood flow in a variable venous congestion murine hind limb model using indocyanine green (ICG, SPY Pack, LifeCell, Branchburg, NJ) angiography. METHODS: Male Sprague-Dawley rats (Charles River, Hudson, NY) underwent bilateral partial amputation at the inguinal ligament, leaving only the femoral vessels and femur intact. Complete unilateral venous occlusion was achieved via suture ligation, while partial occlusion was achieved by surrounding the femoral vein with a synthetic microtube to achieve 25, 75, 85, or 92% occlusion. Relative blood flow of occluded and control limbs was tracked with ICG angiography throughout a 90-minute time course. RESULTS: ICG angiography detected statistically significant (p < 0.05) reductions in limb blood flow 1 and 2 minutes following ICG injection in the 100, 92, and 85% occluded limbs when compared with contralateral control limbs. Dynamic tracking using the slope of ICG inflow for 45 seconds postinjection reflected this same significant difference. No statistically significant change in limb blood flow or dye influx rate was observed in the 25 and 75% occlusion groups. CONCLUSIONS: ICG angiography can detect venous congestion in a rat lower extremity model reliably at occlusion rates ≥ 85%. This method may offer surgeons an intraoperative diagnostic tool to identify venous congestion at extremely early time points, allowing for immediate intervention. Further investigation and characterization is warranted in a larger animal model before clinical adaptation.