The article redefines the diagnosis of iron deficiency in patients with chronic heart failure (CHF). Historically, serum ferritin levels <115 to 20 μg/L indicated absent bone marrow iron stores, but these levels are distorted in patients with CHF due to systemic inflammation. As a result, the diagnostic threshold was increased to <100 μg/L for patients with chronic kidney disease, regardless of transferrin saturation (TSAT). However, this definition is not reliable for identifying iron deficiency in CHF patients, as it includes individuals with normal TSAT and serum ferritin levels who do not respond well to iron therapy. The authors propose that the current ferritin-driven definition should be abandoned and replaced with a definition based on hypoferrremia (TSAT <20%), which is more evidence-based and has shown better outcomes in patients with CHF. They argue that the most reliable indicator of iron deficiency is the response to intravenous iron therapy, which can improve exercise tolerance and functional capacity and reduce the risk of cardiovascular events. The article also discusses the confounding effects of drugs used in CHF treatment, such as neprilysin inhibitors and sodium-glucose cotransporter 2 inhibitors, which can distort iron biomarker levels.The article redefines the diagnosis of iron deficiency in patients with chronic heart failure (CHF). Historically, serum ferritin levels <115 to 20 μg/L indicated absent bone marrow iron stores, but these levels are distorted in patients with CHF due to systemic inflammation. As a result, the diagnostic threshold was increased to <100 μg/L for patients with chronic kidney disease, regardless of transferrin saturation (TSAT). However, this definition is not reliable for identifying iron deficiency in CHF patients, as it includes individuals with normal TSAT and serum ferritin levels who do not respond well to iron therapy. The authors propose that the current ferritin-driven definition should be abandoned and replaced with a definition based on hypoferrremia (TSAT <20%), which is more evidence-based and has shown better outcomes in patients with CHF. They argue that the most reliable indicator of iron deficiency is the response to intravenous iron therapy, which can improve exercise tolerance and functional capacity and reduce the risk of cardiovascular events. The article also discusses the confounding effects of drugs used in CHF treatment, such as neprilysin inhibitors and sodium-glucose cotransporter 2 inhibitors, which can distort iron biomarker levels.