Background: Anaemia is common among patients with heart failure (HF) and is an important prognostic marker. Aim: We sought to determine the prognostic importance of anaemia in a large multinational pooled dataset of prospectively enrolled HF patients, with the specific aim to determine the prognostic role of anaemia in HF with preserved and reduced ejection fraction (HF-PEF and HF-REF, respectively). Design: Individual person data meta-analysis. Methods: Patients with haemoglobin (Hb) data fromthe MAGGIC dataset were used. Anaemia was defined as Hb < 120 g/l in women and <130 g/l inmen. HF-PEF was defined as EF ≥ 50%; HF-REF was EF < 50%. Cox proportional hazardmodelling, with adjustment for clinically relevant variables, was undertaken to investigate factors associated with 3-year all-causemortality. Results: Thirteen thousand two hundred and ninety-five patients with HF from 19 studies (9887 with HF-REF and 3408 with HF-PEF). The prevalence of anaemia was similar among those with HF-REF and HF-PEF (42.8 and 41.6% respectively). Compared with patients with normal Hb values, those with anaemia were older, were more likely to have diabetes, ischaemic aetiology, New York Heart Association class IV symptoms, lower estimated glomerular filtration rate and were more likely to be taking diuretic and less likely to be taking a beta-blocker. Patients with anaemia had higher all-cause mortality (adjusted hazard ratio [aHR] 1.38, 95% confidence interval [CI] 1.25-1.51), independent of EF group: aHR 1.67 (1.39-1.99) in HFPEF and aHR 2.49 (2.13-2.90) in HF-REF. Conclusions: Anaemia is an adverse prognostic factor in HF irrespective of EF. The prognostic importance of anaemia was greatest in patients with HF-REF.