Exercise oscillatory breathing (EOB) is a ventilatory abnormality that occurs in approximately 20% of heart failure (HF) patients and carries a very unfavourable prognosis.

Pathophysiology seems quite complex and putative mechanisms include increased pulmonary capillary pressure and pulmonary vasoconstriction, circulatory blood-flow fluctuations in the pulmonary arterial system and instability of ventilatory control.

Inhibition of the phosphodiesterase 5 (PDE5) isoenzyme favourably regulates pulmonary vascular tone and permeability through over signaling of the endothelial nitric oxide pathway. The investigators tested the hypothesis that sildenafil would reverse the EOB pattern in patients with HF and pulmonary hypertension.

Inclusion Criteria:

• consent to participate in the study after detailed information about benefits and risks
• negative exercise stress test prior to study initiation
• forced expiratory volume in 1 sec/forced vital capacity ratio >70%;
• LVEF < 45%.

Exclusion Criteria:

• inability to complete a maximal exercise test
• resting systolic blood pressure > 140 or <110 mmHg
• therapy with nitrate preparations
• history of sildenafil intolerance
• significant lung or valvular diseases
• neuromuscular disorders or peripheral vascular disease