The two studies - IRONOUT with oral iron and EFFECT-HF with IV ferric carboxymaltose - evaluated similar endpoints. A convenient and easy-to-use oral iron supplement failed to show any improvement in functional capacity and other endpoints, while IV iron complex tested in HF patients with and without anemia significantly improved peak oxygen uptake (VO2) when compared with standard of care. Oral iron does not work in patients with HF because it is not adequately absorbed. In addition to EFFECT-HF, two previous studies, FAIR-HF and CONFIRM-HF, have shown that IV iron supplementation can improve 6-minute walk distance and quality-of-life and decrease HF hospitalizations.