Iron deficiency is a significant comorbidity of heart failure (HF), defined as the inability of the myocardium to provide sufficient blood flow. However, iron deficiency remains insufficiently detected. Iron-deficiency anemia, defined as a decrease in hemoglobin caused by iron deficiency, is a late consequence of iron deficiency, and the symptoms of iron deficiency, which are not specific, are often confused with those of HF or comorbidities. HF patients with iron deficiency are often rehospitalized and present reduced survival. The correction of iron deficiency in HF patients is associated with improved functional capacity, quality of life, and rehospitalization rates. Because of the inflammation associated with chronic HF, which complicates the picture of nutritional deficiency, only the parenteral route can bypass the tissue sequestration of iron and the inhibition of intestinal iron absorption. Given the negative impact of iron deficiency on HF progression, the frequency and financial implications of rehospitalizations due to decompensation episodes, and the efficacy of this supplementation, screening for this frequent comorbidity should be part of routine testing in all HF patients. Indeed, recent European guidelines recommend screening for iron deficiency (serum ferritin and transferrin saturation coefficient) in all patients with suspected HF, regular iron parameters assessment in all patients with HF, and intravenous iron supplementation in symptomatic patients with proven deficiency. We thus aim to summarize all currently available data regarding this common and easily improvable comorbidity.