Exercise Intolerance in Heart Failure

Eligibility Details: 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