• Adult (≥18 years of age) able to provide informed consent.

• Stable heart failure (NYHA II-IV) for at least 4 weeks

• Heart Failure with Preserved left ventricular ejection fraction.(Left ventricular ejection fraction ≥ 50 % obtained within 6 months of informed consent.

• NT-proBNP ≥ 125 pg/mL without ongoing atrial fibrillation/flutter. If ongoing atrial fibrillation/flutter at the time of sample collection, NT-proBNP must be ≥ 250 pg/mL OR patients must have a history of pulmonary capillary wedge pressure ≥ 15 mm Hg during rest or the slope of pulmonary capillary wedge pressure to cardiac output (PCWP/CO) ≥ 2.0 mmHg/L/min during upright exercise (Eisman et al., Circ Heart Fail. 2018 May;11(5):e004750.).OR subjects must have a heart failure hospitalization within the last 12 months prior to screening OR Chronic diastolic dysfunction on echocardiography as evidenced by: Left Atrial Enlargement (LAE): LA diameter ≥ 3.8cm in women, ≥ 4.0 cm in men or LA length ≥ 5.0 cm or LA area ≥ 20 cm2 OR LA volume ≥ 55mL or LA volume index ≥ 29ml/m2 or Left Ventricular Hypertrophy (LVH): septal thickness or posterior wall thickness ≥ 1.1 cm OR For patients in sinus rhythm: E/e' ratio ≥15 at septal annulus, or E/e' ratio ³13 at lateral annulus, or average E/e' ratio ³14. For patients in atrial fibrillation: E/e' ≥ 11 at the septal annulus.

• Hemoglobin \>9.0 g/dL AND \<15.0 g/dL .

• Serum ferritin \<100 ng/mL OR 100 to 300 ng/mL with TSAT \<20%, but NOT ferritin \< 15 ng/mL.

• Demonstrate diminished exercise capacity: ≤ 75 % predicted peak VO2 as determined by a Cardiopulmonary Exercise Test (CPET) at the time of screening

• Perform a maximal effort CPET by achieving a Respiratory Exchange Ratio (RER) of ≥ 1.05