Inclusion Criteria:
* Patients of either gender who are greater than 21 years of age (no upper age limit),
* Permission of patient's clinical attending physician,
* Previous clinical diagnosis of HF with current New York Heart Association (NYHA) Class II-III symptoms for at least 1 month,
* Left ventricular ejection fraction (EF) \>50% by echocardiography, MRI, CT or x-ray or nuclear ventriculography within prior 12 months,
* Stable medical therapy for at least 30 days (no addition or removal or major (\>100%) dose change of Renin-Angiotensin-Aldosterone System (RAAS) antagonists, beta-blockers, or calcium channel blockers for hypertension).
Exclusion Criteria:
* Unable to understand the risks, benefits, and alternatives of participation and give meaningful consent,
* Contraindications to MRI such as implanted metallic objects (pre-existing cardiac pacemakers, cerebral clips) or indwelling metallic projectiles,
* Significant valvular abnormalities,
* Pregnant women (women of childbearing potential will undergo blood or urine pregnancy testing),
* History of clinical CAD or significant epicardial coronary disease (\>50% stenosis) in major coronary artery by x-ray or CT angiography unless (a) the patient underwent prior successful revascularization with percutaneous coronary angioplasty within the prior three years and (b) there are no residual lesions of \>50% on the most recent coronary angiographic study.
* History of infiltrative cardiomyopathy or constrictive pericarditis,
* Cor pulmonale,
* Significant pulmonary disease,
* Estimated glomerular filtration rate (eGFR) \<20ml/min,
* Any condition other than HF which could limit the ability to perform a 6MW or cardiopulmonary exercise test (CPET) test (e.g., critical peripheral vascular disease, significant orthopedic or neurological conditions),
* Any diseases other than HF which are likely to significantly alter the patient's global perception of status or quality of life over a period of 6 months.
* Significant peripheral vascular disease
