| - For many microsurgeons, antegrade internal mammary vessels (AIMVs) represent the recipients of choice in autogenous breast reconstruction. For the past few years, the retrograde internal mammary vessels (RIMVs) have been demonstrated to be a further reliable option when needed, according to many papers focusing more on the vein than on the artery. Besides the clinical evidence, the hemodynamic features of the retrograde system have been very seldom analyzed.In this article, we report our clinical experience with deep inferior epigastric perforator (DIEP) flaps anastomosed to RIMVs, along with a perioperative radiological follow-up to study RIMVs' hemodynamics and to further support the reliability of the retrograde system with particular focus on the retrograde internal mammary artery.Prospective, preoperative, and postoperative (3 days, 21 days, and 3 months, respectively) color Doppler sonographies of the internal mammary artery (IMA) and DIEPs have been performed to collect the velocity of flow (v) and resistive index (RI) data. Twenty-two patients agreed to undergo this protocol, of which 10 unipedicle flaps were anastomosed to AIMVs ("control" group), 10 bipedicle DIEPs to both AIMVs and RIMVs ("study" group), and 2 DIEPs anastomosed to retrograde internal mammary artery and antegrade internal mammary vein (not statistically analyzed for their paucity). Student t test was performed to compare the "control" and "study" groups.All the flaps survived, and no re-exploration was needed. Internal mammary artery and perforators v showed similar but speculate trend, whereas IMA and perforators RI looked stable during that time. Significant differences have been found in the "study" group for IMA v at 3-day period, for perforator v at 21- and 90-day periods, and for perforator RI at 90-day period, without any clinical implication for flap viability.Retrograde internal mammary vessels can be considered reliable vessels for both arterial flap input and venous flap outflows, either as additional or the sole recipients. However, further and larger studies would be useful to better understand the hemodynamics of the retrograde system.