The overall purpose of this study is to determine if weight loss is beneficial for obese patients with diastolic heart failure.

Inclusion Criteria:

• All subjects will have obesity and have a BMI > 35kg/m2.
• Subjects must be between the ages of 35 and 65 years, in order to limit the confounding affect of age on our endpoints.

To determine if potential subjects meet these criteria, they will:

1. be interviewed,
2. their clinical charts reviewed, by the research study coordinator and/or the PI, and
3. undergo a history and physical by a physician (Study Day 2). Subjects who are to undergo gastric bypass surgery will be in the intervention arm. They will be matched with control subjects. We will attempt to have no more than one control subject for each gastric surgery subject.

Exclusion Criteria:

• Subjects who have a condition that may masquerade as diastolic heart failure will be excluded (see Research and Design).
• Subjects who are < 35 or > 65 years, > 400lbs (the weight limit of the MRI table) not obese, unstable, not able to lie flat for the imaging studies, not ambulatory, unable to give informed consent, pregnant, lactating, with atrial flutter or fibrillation, current smokers, or who will undergo a different type of bariatric surgery (not Roux-en-Y gastric bypass) will be excluded from participation.
• Those who have evidence of other major systemic diseases (e.g., cancer, significant lung disease, creatinine > 2.0mg/dL, hemoglobin < 10g/dL, and liver function tests twice the normal range) will be excluded.
• Subjects who have > class I hypertension will be excluded. The investigators will exclude patients with an LV ejection fraction < 45% and those with significant pulmonary hypertension (peak artery pressure > 55mmHg).

Patients who are obese with heart failure and will undergo gastric bypass surgery or who have already had gastric bypass surgery.