Iron deficiency is a widely prevalent finding in patients with heart failure, observed on average in 50% of outpatients and up to 80% of acute patients, regardless of the ejection fraction and the presence of anemia, being an independent predictor of worst functional capacity and reduced survival. The definition of iron deficiency in heart failure considers the state of chronic inflammation that characterizes the pathology, recognizing a discriminating role for transferrin saturation. The studies conducted so far, which focused on the patient with heart failure with at least moderately reduced ejection fraction, have shown clinical benefit with intravenous supplementation of ferric carboxymaltose in terms of functional capacity, quality of life, laboratory markers of disease and inflammation, and possible reduction of re-hospitalizations, but not in terms of mortality. Based on this evidence, guidelines recommend intravenous ferric carboxymaltose in decompensated and iron-deficient patients, while research is at work to investigate the clinical impact of supplementation in contexts not yet examined, such as that of decompensation in patients with heart failure and preserved ejection fraction.