Heart failure (HF) with preserved ejection fraction (HFpEF) occurs in about 50% of all HF patients. Remodeling and fibrosis stimulated by inflammation appear to be main factors for the progression of HFpEF. Furthermore, iron deficiency (ID) has been recognized to be a common comorbidity in HFpEF. The lack of prognostic treatment options in HFpEF urgently calls for new therapeutic approaches. While beneficial effects of exercise training and iron substitution have been demonstrated in HF with reduced ejection fraction, they have not yet been evaluated in HFpEF. Therefore, the aim of this study is to investigate the effects of high-intensity interval training (HIT) in HFpEF patients with optimally adjusted iron values.