Funding: This work was supported in part by an unrestricted grant from Vifor Pharma and Proyectos de Investigación de la Sección de Insuficiencia Cardiaca 2017 from Sociedad Española de Cardiología.

The mechanisms underlying the beneficial effect of ferric carboxymaltose (FCM) in patients with heart failure (HF) and iron deficiency (ID) have not been completely characterized. The Myocardial-IRON trial was a double-blind, randomized trial that evaluated myocardial iron repletion following FCM vs. placebo in 53 patients with HF and ID. In this post hoc analysis, we evaluated whether treatment with FCM was associated with cardiac magnetic resonance changes in left and right ventricular function (LVEF and RVEF, respectively) at different points of systolic dysfunction. We included patients from the Myocardial-IRON trial with left and right ventricular systolic dysfunction (LVSD and RVSD, respectively) at enrolment. Linear mixed regression models were used to evaluate changes at 7 and 30 days on LVEF and RVEF at cardiac magnetic resonance. At enrolment, 27 (50.9%) and 38 (71.7%) patients had LVEF < 40% (LVSD) or <45% (LVSD), respectively, and 10 (18.9%) and 17 (32.1%) patients had RVEF < 45% (RVSD) or <51% in women and <52% in men (RVSD, respectively. Treatment with FCM was associated with a significant improvement in LVEF at 30 days (LVSD: Δ2.3%, P < 0.001; LVSD: Δ4.1, P = 0.014). FCM was also associated with a significant and early improvement in RVEF at 7 days (RVSD: Δ6.9%, P = 0.003; RVSD: Δ3.2%, P = 0.003) that persisted at 30 days (RVSD: Δ8.1%, P < 0.001; RVSD: Δ4.7%, P < 0.001). In patients with HF and systolic dysfunction with ID, FCM was associated with short-term improvement in LVEF and, especially, in RVEF.