The proposed study will be a prospective, single-blind, randomized controlled trial in a primary care setting including 98 patients with stable HFpEF. Patients will undergo 3 study visits (a screening visit, a baseline visit and a post-intervention visit) including measurements of disease-specific biomarkers (using blood samples), cardiac and arterial vessel structure and function (using electrocardiogram, echocardiography and pulse wave velocity), exercise tolerance (using spiroergometry), habitual physical activity (using accelerometry) and QoL. After the screening visit, patients with a functional or absolute ID will undergo iron substitution until sufficient iron levels are reached (up to max. 12 weeks), in order to ensure comparable baseline conditions for the training intervention. The study examinations will be repeated after 12 weeks in both, initially iron deficient and non-iron deficient patients (baseline visit). Patients will then be randomized to either the intervention or control group, stratified by initial iron-deficiency status. The intervention group (n=49) will attend a supervised 12-week HIT on a bicycle ergometer, while the control group (n=49) will be advised to continue usual care and follow health recommendations for patients with chronic HF. After 12 weeks, the study measurements will be repeated in all patients (intervention and control group) in order to monitor the effects of the intervention (post-intervention visit). At 6 months, 1, 2 and 3 years after the last study visit, telephone interviews will be performed to assess medical outcomes and QoL.