Patients with heart failure have elevated levels of circulating inflammatory cytokines and commonly have iron deficiency anemia or anemia of chronic inflammation. Clinical trials in patients with congestive heart failure and iron deficiency have demonstrated that intravenous iron treatment appears to improve subjective and objective outcomes. Most patients in these trials were not anemic or only had mild anemia, and hemoglobin concentration rose only slightly after treatment with iron. Experimental evidence demonstrates that iron is a cofactor for muscle function, which could explain the improvement in clinical outcomes. Many questions remain to be answered to understand the role of iron therapy in patients with congestive heart failure.