BACKGROUND: Anemia in heart failure patients and has been associated with increased morbi-mortality. Previous studies have treated anemia in heart failure patients with either erythropoietin alone or combination of erythropoietin and intravenous (i.v.) iron. However, the effect of i.v. or oral (p.o.) iron supplementation alone in heart failure patients with anemia was virtually unknown. AIM: To compare, in a double-blind design, the effects of i.v. iron versus p.o. iron in anemic heart failure patients. METHODS: IRON-HF study was a multicenter, investigator initiated, randomized, double-blind, placebo controlled trial that enrolled anemic heart failure patients with preserved renal function, low transferrin saturation (TSat) and low-to-moderately elevated ferritin levels. Interventions were Iron Sucrose i.v. 200 mg, once a week, for 5 weeks, ferrous sulfate 200 mg p.o. TID, for 8 weeks, or placebo. Primary endpoint was variation of peak oxygen consumption (peak VO2) assessed by ergospirometry over 3 month follow-up. RESULTS: Eighteen patients had full follow-up data. There was an increment of 3.5 ml/kg/min in peak VO2 in the i.v. iron group. There was no increment in peak VO2 in the p.o. iron group. Patients' ferritin and TSat increased significantly in both treated groups. Hemoglobin increased similarly in all groups. CONCLUSION: I.v. iron seems to be superior in improving functional capacity of heart failure patients. However, correction of anemia seems to be at least similar between p.o. iron and i.v. iron supplementation.