Effect of Intravenous FerRic carbOxymaltose oN Reverse Remodeling Following Cardiac Resynchronization Therapy

Inclusion Criteria: 1. Chronic heart failure and implantation of cardiac resynchronization therapy more than 6 months ago and presence of iron deficiency (ferritin \< 100 μg/l, irrespective of TSAT or ferritine between 100 - 300 μg/l with TSAT \< 20%) and presence of incomplete reverse remodeling (LVEF \< 40%). 2. Age ≥18 years 3. Obtained informed consent 4. Stable pharmacological therapy of heart failure during the last 4 weeks (with the exception of diuretics) Exclusion Criteria: 1. Hemochromatosis, iron overload, defined as TSAT \> 45% 2. Hemoglobin \> 15 g/dl at inclusion 3. Known hypersensitivity to injectafer®. 4. Known active infection, CRP\>20 mg/L, clinically significant bleeding, active malignancy. 5. Chronic liver disease and/or screening alanine transaminase (ALT) or aspartate transaminase (AST) above three times the upper limit of the normal range. 6. Immunosuppressive therapy or renal dialysis (current or planned within the next 6 months). 7. History of erythropoietin, i. v. or oral iron therapy, and blood transfusion in previous 12 weeks and/or such therapy planned within the next 6 months. 8. Unstable angina pectoris as judged by the investigator, clinically significant uncorrected valvular disease or left ventricular outflow obstruction, obstructive cardiomyopathy, poorly controlled fast atrial fibrillation or flutter, poorly controlled symptomatic brady- or tachyarrhythmias. 9. Acute myocardial infarction or acute coronary syndrome, transient ischemic attack or stroke within the last 3 months. 10. Coronary-artery bypass graft, percutaneous intervention (e.g. cardiac, cerebrovascular, aortic; diagnostic catheters are allowed) or major surgery, including thoracic and cardiac surgery, within the last 3 months. 11. Inability to fully comprehend and/or perform study procedures in the investigator's opinion. 12. Vitamin B12 and/or serum folate deficiency according to the laboratory (re-screening is possible after substitution therapy). 13. Pregnancy or lactation. 14. Participation in another clinical trial within previous 30 days and/or anticipated participation in another trial during this study. 15. Planned cardiac hospitalization during study follow-up