Inclusion Criteria:  HFpEF: Left ventricular ejection fraction ≥ 50%, NT-pro-BNP ≥ 125ng/l, evidence of structural heart diseases (diastolic dysfunction, left ventricular-hypertrophy or left atrial-dilatation), BMI ≥ 30kg/m² Non-HF patients: No history of heart failure, Left ventricular ejection fraction > 50% and NT-pro-BNP <125ng/l  Exclusion Criteria:  Previous cardiac surgery / coronary intervention / myocardial infraction Acute coronary syndrome (Serum levels of troponin T >50 pg/ml) Left ventricular ejection fraction < 50% Indication for concomitant valvular surgery Planned beating heart coronary bypass surgery Hemodynamic instability Contraindication for magnetic resonance imaging Pregnancy Age < 18 years No informed consent possible