The primary purpose of this study is to test whether the dapagliflozin (Dapa) will improve exercise duration in people with Heart Failure (HF). In HF, patients are limited in their ability to do all the things they want to do, and exercise as much as they would like, due to becoming tired and short of breath early. We do not know exactly why these limitations occur. In addition to determining whether Dapa improves exercise duration, testing in this study is also designed to determine how these improvements might occur. Many patients with HF also have problems with their arteries, muscles and liver that may affect their ability to exercise. The planned measurements obtained using echocardiography, blood testing, MRI scanning and muscle biopsy (optional) are designed to show us how Dapa may be working.

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

• Conditions: Medical Research, Heart Failure
• Age: 18 years - 99 years
• Gender: All