 Rationale: Treatment of diastolic left heart failure is a challenging task. Compared to systolic left heart failure the level of evidence for known medical treatment regiments is low. Sildenafil, a phosphodiesterase 5 PDE 5 inhibitor and effective therapy for pulmonary arterial hypertension acts as a selective pulmonary vasodilator by inhibiting the impaired nitric oxide NO pathway. Reducing the pulmonary vascular resistance would be the primary target by treatment of diastolic left heart failure with PH. But clinical and hemodynamical studies to evaluate the role of Sildenafil in diastolic heart failure, also called heart failure with preserved ejection fraction HFpEF with secondary pulmonary hypertension are lacking. Our hypothesis is that Sildenafil decreases pulmonary artery pressure in patients with HFpEF and pulmonary hypertension. 