Motivation: Determining the impact of iron repletion on muscle energetics in non-ischaemic cardiomyopathy with reduced ejection fraction (EF). Goal(s): Use cardiac and skeletal muscle 31P MRS to assess cardiac and skeletal muscle energetics pre and post iron repletion therapy. Approach: Participants and ID underwent CMR to assess cardiac function, MRS to assess Phosphocreatine to Adenosine triphosphate (PCr/ATP) ratio in cardiomyocyte and relation to skeletal muscle PCr consumption, end-exercise intracellular pH and PCr recovery rate before and after Ferric carboxymaltose (FCM). Results: FCM improves ejection fraction, 6-minute-walk-distance. It didn’t change in myocardial resting or dynamic energetics or skeletal muscle oxidative metabolism. Impact: Iron infusion didn’t change PCr/ATP, however increased left ventricular ejection fraction, therefor increase ATP requirement. We hypothesise that iron replacement resulted in increase in energy efficiency, or improved flux through Creatine Kinase, which was not assessed during this study.