<br>        Inclusion Criteria:<br><br>          -  Patients in good and stable health condition<br><br>          -  Informed consent has to be given in written form<br><br>          -  HFpEF in stable conditions according to 2016 ESC guidelines definition14<br><br>               -  LVEF = 50%<br><br>               -  symptoms and/or signs of CHF<br><br>               -  NT-proBNP > 125 pg/ml<br><br>               -  At least one additional criterion: relevant structural heart disease (left<br>                  ventricular hypertrophy and/or left atrial enlargement and/or diastolic<br>                  dysfunction<br><br>        Exclusion Criteria:<br><br>          -  Uncontrolled diabetes (fasting plasma glucose = 240 mg/dl, HbA1c = 10%)<br><br>          -  Uncontrolled arterial hypertension (= 180/110 mmHg)<br><br>          -  Any history of stroke, transient ischemic attack, instable angina pectoris or<br>             myocardial infarction within the last 6 months prior to study inclusion<br><br>          -  Significant valvular heart disease<br><br>          -  Known hypertrophic obstructive cardiomyopathy or known pericardial constriction<br><br>          -  Atrial fibrillation with a resting heart rate > 90 bpm<br><br>          -  Heart transplant recipient<br><br>          -  Sickle cell anemia<br><br>          -  Pheochromocytoma<br><br>          -  Myasthenia gravis<br><br>          -  Subclinical or clinical hyperthyroidism<br><br>          -  Allergic reaction to iodine<br><br>          -  Medication with amiodarone<br><br>          -  Estimated glomerular filtration rate < 30 ml/min/1.73m²<br><br>          -  Significant laboratory abnormalities such as Serum Glutamate-Oxaloacetate-Transaminase<br>             (SGOT) or Serum Glutamate-Pyruvate-Transaminase (SGPT) levels more than 3 times above<br>             the upper limit of normal range<br><br>          -  Patients in unstable conditions due to any kind of serious disease, that infers with<br>             the conduction of the trial<br><br>          -  History of epilepsia and history of seizures<br><br>          -  Patients suffering from cataract or glaucoma<br><br>          -  Diabetic retinopathy<br><br>          -  Drug or alcohol abuse<br><br>          -  Pregnant and breast-feeding patients<br><br>          -  Body mass index > 40 kg/m²<br><br>          -  Participation in another clinical study within 30 days prior to visit 1<br><br>          -  Individuals at risk for poor protocol adherence<br><br>          -  Subjects who do not give written consent, that pseudonymous data will be transferred<br>             in line with the duty of documentation and the duty of notification according to § 12<br>             and § 13 GCP-V<br>