The goal of this clinical trial is to evaluate if a bariatric surgery strategy will improve clinical endpoints, cardiac parameters and functional status in patients with obesity (with BMI 32-40 kg/m2) and symptomatic HF with preserved or mildly reduced LVEF in combination with AF, as compared to standard of care. Patients will be randomized to either the Intervention group receiving bariatric surgery including an intensive pre- and postoperative treatment scheme or to the control group receiving standard of care.

The primary objective is to study the effect of a bariatric surgery strategy on the hierarchical occurrence of: 1) all-cause mortality within 2 years, 2) emergency room visit or hospitalization for HF within 2 years, 3) recurrent ECG-documented AF within 2 years, 4) decrease of ≥30gr of left ventricular (LV) mass on transthoracic echocardiography, and 5) improvement of ≥5 points on the Kansas City Cardiomyopathy Questionnaire (KCCQ).

Inclusion Criteria:

1. Signs and symptoms of HF according to the Europeans Society of Cardiology guideline;
2. Left ventricular ejection fraction ≥40%;
3. HFA-PEFF score ≥5 or HFA-PEFF score 2-4 in combination with positive stress test;
4. Between 45 and 70 years of age;
5. BMI 32-40 kg/m2;
6. Paroxysmal or persistent AF with a rhythm control strategy;
7. Willing to undergo both treatment strategies;
8. Written informed consent.

Exclusion Criteria:

1. BMI ≥40 kg/m2;
2. BMI <32 kg/m2;
3. Patients unwilling or unable to sign informed consent;
4. More than moderate mitral valve regurgitation/aortic valve regurgitation;
5. More than mild mitral valve stenosis/aortic valve stenosis;
6. Inadequate echocardiographic window for the assessment of LV mass index and/or the echocardiographic criteria needed for the HFA-PEFF score;
7. History of myocardial infarction, myocarditis, any invasive cardiac intervention (e.g. surgery, percutaneous coronary intervention, ablation) or stroke, <3 months before inclusion;
8. Scheduled for AF ablation;
9. Complex congenital heart disease;
10. Negative treatment advise from a specialized psychiatrist due to non-stabilized psychotic disorders, severe depression and/or personality disorders;
11. Patients unable to care for themselves or who are unable adapt to inherent lifestyle changes following bariatric surgery;
12. Any medical condition that limits life span <2 years;
13. Diseases requiring long term use of anti-inflammatory treatments;
14. The use of medication associated with substantial effects (>5 kg) on body weight.