Single Iron Infusion Improves Exercise Capacity in Common Form of Heart Failure

A single intravenous iron infusion has measurably restored the ability to exercise and perform daily tasks for patients living with a common, restrictive form of heart failure. The intervention targets an underlying iron deficiency that limits oxygen delivery, offering a rapid functional improvement without adding another daily pill to complex medication regimens.[1][2]

The findings come from the IRON-MET HFpEF trial, presented this week at the 2026 American Heart Association Scientific Sessions in Chicago and published simultaneously in the journal Circulation. Researchers at the Mass General Brigham Heart and Vascular Institute demonstrated that a 1,000-milligram dose of ferric derisomaltose improved peak oxygen uptake by approximately 10 percent over 12 weeks.[1][2][4]

Heart failure with preserved ejection fraction, or HFpEF, occurs when the heart pumps a normal proportion of blood but struggles to relax and fill properly between beats. The condition affects roughly half of all heart failure patients, leading to severe breathlessness, fluid congestion, and fatigue during routine activities like climbing stairs or walking.[4][5]

Iron deficiency compounds this exhaustion, affecting more than 50 percent of individuals diagnosed with HFpEF. Because iron is essential for transporting oxygen through the blood and generating energy within muscle cells, a systemic shortage leaves patients physically drained even when their primary cardiac condition is otherwise medically managed.[1][2]

Bypassing the digestive system

Oral iron supplements are notoriously ineffective for this patient population, largely due to poor gastrointestinal absorption caused by the heart failure itself. Fluid congestion in the gut wall and elevated systemic inflammatory markers block the body from taking up iron pills, leaving patients deficient despite daily supplementation efforts.[1][2]

To bypass this absorption barrier, the trial utilized MonoFerric, an intravenous formulation that delivers a high dose of iron directly into the bloodstream. The study enrolled 65 participants with symptomatic HFpEF and confirmed iron deficiency, randomizing 44 to receive the active infusion and 21 to a placebo group.[1][4]

"In the first study to comprehensively evaluate exercise response patterns to iron repletion in patients with HFpEF and iron deficiency, we found that ferric derisomaltose improved multiple measures of exercise capacity," said Dr. Gregory D. Lewis, director of Heart Failure at Mass General Brigham.[1][2]

The cohort, which had a median age of 68 and was 72 percent female, underwent rigorous cardiopulmonary exercise testing before the infusion and again 12 weeks later. The primary metric was peak oxygen uptake, or VO2, which serves as a definitive clinical indicator of overall cardiorespiratory fitness and disease burden.[1][2]

Measurable gains in physical capacity

At the 12-week mark, patients who received the intravenous iron saw their peak VO2 improve by about 10 percent, while the placebo group experienced no change. This increase translates directly into a greater ability to sustain physical exertion without becoming immediately breathless, restoring a margin of independence.[1][2][3]

"The improvement we observed in peak VO2 represents a clinically meaningful increment for patients with heart failure," noted Dr. Rajeev Malhotra, associate director of the Cardiopulmonary Exercise Laboratory at Mass General Brigham and co-principal investigator of the trial.[4][5]

Beyond peak oxygen uptake, the intervention group also demonstrated improvements in several secondary measures of physical function. These included the total distance they could walk in six minutes and their oxygen uptake at the anaerobic threshold, the point during exercise when lactic acid begins to build up in the blood.[1][3]

Blood tests confirmed that the bioavailability of iron increased significantly in the treated patients, proving that the intravenous delivery successfully replenished systemic stores. The treatment was also well tolerated, with researchers reporting no serious adverse events linked to the single high-dose infusion during the study window.[1][3]

The cellular role of iron

The success of the infusion highlights a critical mechanism in cardiovascular disease, demonstrating that iron is not just for making red blood cells. It is a vital component of the mitochondria, the microscopic powerhouses within skeletal and cardiac muscle cells that generate the energy required for sustained physical movement.[3]

When iron levels drop, these cellular engines cannot produce energy efficiently, leading to the profound muscle weakness that heart failure patients frequently experience. By rapidly restoring iron stores intravenously, the therapy effectively repairs the metabolic machinery in the muscles, allowing them to extract and utilize oxygen more effectively during exertion.[3]

Historically, clinical trials testing intravenous iron have focused primarily on heart failure with reduced ejection fraction, where the heart muscle is actively weakened and fails to pump forcefully. Those earlier studies established iron repletion as a standard of care for that specific group, but its role in preserved ejection fraction remained largely untested until now.[4]

Because HFpEF is driven more by the stiffening of the heart muscle and systemic inflammation than by a loss of pumping power, therapies that work for one type of heart failure often fail in the other. Proving that iron repletion works in this distinct physiology closes a significant gap in the evidence base for a difficult-to-treat population.[4]

Translating findings to patient care

For patients currently managing HFpEF, these results emphasize the importance of routine screening for iron deficiency, a step that is often overlooked in standard cardiovascular care. Identifying and treating low iron levels offers a targeted, measurable way to alleviate the profound fatigue that defines the daily experience of the disease.[1][3]

Because the therapy requires an intravenous infusion, patients will need to receive the treatment in a clinical setting rather than picking up a prescription at a pharmacy. However, the single-dose approach means that individuals can achieve lasting functional benefits without the burden of remembering to take daily oral supplements that their bodies cannot absorb.[1][2]

AI

While the physical improvements were clear, the study did note that patient-reported health scores, gathered through comprehensive questionnaires, did not differ significantly between the treatment and placebo groups. This suggests that while patients could objectively do more in a clinical testing environment, their subjective perception of their daily health remained complex.[3]

The trial's relatively small size of 65 participants and its 12-week duration leave some questions open regarding exactly how long the functional benefits of a single infusion will last. The cohort was also predominantly white, prompting the researchers to call for larger, more diverse studies to confirm that the efficacy holds across broader demographic groups.[3]

The path forward for cardiology

The next phase of research will focus on whether intravenous iron therapy can improve long-term clinical outcomes, such as reducing the frequency of hospitalizations for heart failure exacerbations. Preventing these admissions is a primary goal of cardiovascular disease management, as each hospitalization typically signals a decline in a patient's overall trajectory.[3]

Until those larger trials conclude, the current data provides a practical, immediate option for cardiologists treating patients whose lives are restricted by HFpEF and concurrent iron deficiency. A simple blood test to check ferritin levels and transferrin saturation can identify those who might benefit from this targeted repletion strategy.[1][3]

The findings add to a growing consensus in cardiology that managing heart failure requires looking beyond the heart muscle itself to optimize the entire circulatory and metabolic system. Correcting a basic nutritional deficit in the blood can yield physical improvements that rival those of advanced, highly engineered cardiovascular medications.[1][2]

Patients experiencing unexplained worsening of their exercise tolerance should ask their care teams to evaluate their iron indices. If a deficiency is confirmed, a single clinical visit for an infusion could restore a critical margin of physical independence and make daily routines manageable again.[1][2]