Background The latest studies presented at the American Heart Association (AHA) meeting on heart failure and the update of the European Cardiology Society's (ECS) recommendations on heart failure in 2016 recommend intravenous iron supplementation in patients with heart failure, reduced ejection fraction and iron deficiency for improves walking performance and quality of life, and reduces morbidity. In the present study, we investigated the prevalence of iron deficiency in heart failure patients aged 75 years or older, as there is currently no data on these patients. Methods We performed an observational study on hospitalized patients in Geriatric Cardiology Department. Among the 462 patients hospitalized during eight months, 176 were eligible for inclusion; 22 patients was significant interference with an inflammatory syndrome (high ferritin with high C-reactive protein), and for 13 patients iron-related data were not available. For each patient included, a complete iron assessment and type of heart failure was available. Results A total of 141 patients were included, the mean age was 88 years (range: 75-101), and there were 52 (36.9%) of patients with reduced ejection fraction (EF), 37 (26.2%) with mid-range EF, and 52 (36.9%) with preserved EF. Irrespective of heart failure type, 73.8% had iron deficiency (95% CI: 65.7%-80.8%); this was found in 57.7% (95% CI: 43.2%-71.3%) of those with reduced EF, 78.4% (95% CI: 61.8%-90.2%) of those with mid-range EF, and 86.5% (95% CI: 74.2%-94.4%) of those with preserved EF (P = 0.003). Conclusion The prevalence of iron deficiency was very high in very elderly patients with heart failure, especially those with HF with mid-range EF or HF with preserved EF.