Inclusion Criteria:  Age 18 years or older and able to give written informed consent New York Heart Association (NYHA) functional class II or III Left Ventricular Ejection Fraction (LVEF) > 50% Plasma Brain Natriuretic Peptide (BNP) >200 pg/mL or NT-proBNP 400 pg/mL at enrollment  Exclusion Criteria:  Prior EF of <50%. NYHA Class IV or HF that cannot be stabilized on optimized pharmacotherapy Acute coronary syndrome, infiltrative cardiomyopathy, or myocarditis Patients with HFpEF secondary to significant uncorrected primary valvular disease (except mitral regurgitation secondary to left ventricular dysfunction) Orthopedic limitations that would prohibit knee-extensor exercise Women currently taking hormone replacement therapy (HRT) will be excluded from the proposed studies due to the direct vascular effects of HRT Women who are pregnant or may become pregnant, but the typical age of female patients with HFpEF will be postmenopausal Current smokers