Sildenafil is a potent selective phosphodiesterase inhibitor that suppresses degradation of cyclic GMP. In the pulmonary bed this leads to pulmonary vasodilation, in addition sildenafil has been shown to improve endothelium dependent vasodilation thus augmenting abnormal vascular tone . In patients with systolic heart failure sildenafil has been demonstrated to lower pulmonary wedge pressure, improve cardiac index and lower pulmonary arterial pressure without causing systemic hypotension . Thus in theory sildenafil may have beneficial effects in patients at high risk of heart failure.