The study is being conducted to understand why the skeletal muscle of patients with Heart Failure with Preserved Ejection Fraction (HFpEF) does not work as well as the muscle of individuals without heart failure. This study seeks to understand whether the problem is with blood and oxygen delivery to the muscle or with how the skeletal muscle uses the blood and oxygen to make energy. Subjects will be asked to complete the following research procedures: Two research MRI scans of your lower leg (one while breathing room air and one while breathing 100% oxygen) and one six-minute walk test during a one-day visit. There is no potential benefit to subjects, though the information gathered may ultimately help us learn how to treat patients with this condition better. The most common risks of participation are feeling uncomfortable in the MRI scanner due to lying still on the MRI table for prolonged periods of time, feeling claustrophobic in the MRI scanner (although your head will not be in the scanner), and minor leg discomfort from being asked to exercise in the MRI scanner.

You may be eligible for this study if you meet the following criteria:

• Conditions: Medical Research
• Age: 99 years or below
• Gender: All