Physical Activity, Cardiac and Skeletal Muscle Energetics in Healthy Subjects and HFpEF Patients

This study uses specialized MRI and exercise tests to examine how physical activity affects heart and muscle energy production in both healthy individuals with obesity and in patients with a form of heart failure called HFpEF (heart failure with preserved ejection fraction), where the heart squeezes normally but doesn't fill properly. **You may be eligible if...** - You are 40–85 years old - You have a BMI between 30 and 50 - Healthy participants must have no history of diabetes, heart failure, heart attack, or major vascular disease - Heart failure participants must have a confirmed HFpEF diagnosis with symptoms for at least 1 month, on diuretic treatment for at least 30 days, and a preserved ejection fraction (≥50%) **You may NOT be eligible if...** - You have had a heart attack, stroke, or TIA within the past 6 months - You have an active cancer not in remission for 5+ years - You have metal implants or severe claustrophobia preventing MRI - You have very high triglycerides or LDL cholesterol on current medications - You have had weight loss surgery or taken weight loss drugs in the past 6 months - Heart failure patients: you have infiltrative cardiomyopathy, severe valve disease, significant coronary artery disease, or kidney function below a certain threshold Talk to your doctor to see if this trial is right for you.