PURPOSE: The prevalence of iron deficiency (ID) in Left Ventricular Assist Device (LVADs) recipients is not known nor has the association between ID and peak oxygen uptake (VO2) been reported. The aim of this study was to study to investigate the prevalence of ID in this population and the association between ID and VO2. METHODS: Data was included from LVAD recipients at Rigshospitalet, Denmark (DK), and Skåne University Hospital, Lund, Sweden (SE), retrospectively for the prevalence investigation and prospectively between 2013 and 2019 from Rigshospitalet, DK, for the investigation of VO2. Blood samples were collected retrospectively at both sites. ID was defined transferrin saturation (TSAT)≤20%. Anemia was defined as Hb<7.0 mmol/L. RESULTS: TSAT was available from 52 patients (DK: 36, SE: 16) 415±562 days post implantation. Most patients were male (12% female), implanted with a HeartMate(HM) 3 device (72%) and the average age at time of implantation was 56±12years. ID was present in 77% (30% with vs 70% without concurrent anemia, see figure). TSAT was 16±8% in the total cohort. ID (regardless of anemia) was associated with non-ischemic (NICM) HF (R2= 12%, P=0.045) but not age, gender, device indication or N terminal proBNP (P>0.05). The peak VO2 was 47±16% of predicted for age and gender (RER 1.15 (range 0.8 to 1.39), duration: 394±215sec). Linear regression revealed no association between TSAT and VO2 (P=0.5) nor was VO2 lower in patients with ID. After a mean±SD follow up time of 641±721days most patients remained ongoing on device (n=28, 54%), while 14 (27%) were transplanted, 1 was (2%) explanted and 9 (17%) died. Cox regression revealed no difference in survival between patients with ID (TSAT<20%) and those without (P>0.05). CONCLUSION: ID was common in LVADs often with no concurrent anemia, and more prevalent in patients with NICM. ID was not associated with impaired functional capacity or survival.