Venovenous extracorporeal membrane oxygenation (ECMO) can be performed with two single lumen cannulas (SLCs) or one dual-lumen cannula (DLC) where low recirculation fraction (Rf) is a key performance criterion. DLCs are widely believed to have lower Rf , though these have not been directly compared. Similarly, correct positioning is considered critical although its impact is unclear. We aimed to compare two common bi-caval DLC designs and quantify R f in several positions. Two different commercially available DLCs were sectioned, measured, reconstructed, scaled to 27Fr and simulated in our previously published patient-averaged computational model of the right atrium (RA) and venae cavae at 2–6 L/min. One DLC was then used to simulate ± 30° and ± 60° rotation and ± 4 cm insertion depth. Both designs had low Rf (< 7%) and similar SVC/IVC drainage fractions and pressure drops. Both cannula reinfusion ports created a high-velocity jet and high shear stresses in the cannula (> 413 Pa) and RA (> 52 Pa) even at low flow rates. Caval pressures were abnormally high (16.2–23.9 mmHg) at low flow rates. Rotation did not significantly impact Rf . Short insertion depth increased Rf (> 31%) for all flow rates whilst long insertion only increased Rf at 6 L/min (24%). Our results show that DLCs have lower Rf compared to SLCs at moderate-high flow rates (> 4 L/min), but high shear stresses. Obstruction from DLCs increases caval pressures at low flow rates, a potential reason for increased intracranial hemorrhages. Cannula rotation does not impact Rf though correct insertion depth is critical.