Heart failure mystery: scientists probe energy failures in heart and muscles

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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