PURPOSE OF REVIEW: Iron deficiency is common and associated with adverse outcomes in heart failure, regardless of anemia. Iron deficiency, absolute and functional, with and without anemia, is associated with adverse outcomes in chronic kidney disease (CKD). Heart failure and CKD frequently occur together. Intravenous iron therapy has been shown to reduce heart failure symptoms and improve physical function in heart failure with reduced ejection fraction with iron deficiency. In CKD, intravenous or oral iron therapy are often used for management of anemia, along with erythropoiesis stimulating agents, yet the risks and benefits of intravenous iron use is controversial. In this review, we survey available evidence and ongoing studies of iron deficiency and iron supplementation in heart failure, and integrate with recent evidence on effectiveness and safety of intravenous iron therapy in CKD. RECENT FINDINGS: Intravenous iron therapy improves heart failure symptoms and physical function in heart failure with reduced ejection fraction and iron deficiency, regardless of anemia, and may reduce heart failure hospitalizations and cardiovascular mortality. Sustained intravenous iron therapy regardless of hemoglobin level in selected patients with end-stage kidney disease receiving hemodialysis improves outcomes, and does not appear to cause infectious complications. SUMMARY: Iron therapy has important effects in heart failure and CKD, and appears safe in the short term. Ongoing trials will provide additional important information.