* requirement of therapy with nitrates of nitrites * arterial hypotension at presentation * recent diagnosis of coronary artery disease (\<6 months) * acute heart failure at presentation * recent stroke (\< 6 months) * chronic respiratory failure with co2 retention * known hypersensitivity to sildenafil * advanced liver disease (child-pugh class b or higher) * users of cytochrome p450 3a4 inhibitors (erythromycin, ketoconazole, itraconazole, saquinavir) * pulmonary hypertension * chronic users of phosphodiesterase 5 inhibitors * requirement of invasive mechanical ventilation at baseline * decision to limit therapeutic efforts at baseline * pregnancy or lactation * history of retinitis pigmentosa * known obstruction to left-ventricular outflow tract * unwillingness to participate in the trial

* requirement of therapy with nitrates of nitrites * arterial hypotension at presentation * recent diagnosis of coronary artery disease (\<6 months) * acute heart failure at presentation * recent stroke (\< 6 months) * chronic respiratory failure with co2 retention * known hypersensitivity to sildenafil * advanced liver disease (child-pugh class b or higher) * users of cytochrome p450 3a4 inhibitors (erythromycin, ketoconazole, itraconazole, saquinavir) * pulmonary hypertension * chronic users of phosphodiesterase 5 inhibitors * requirement of invasive mechanical ventilation at baseline * decision to limit therapeutic efforts at baseline * pregnancy or lactation * history of retinitis pigmentosa * known obstruction to left-ventricular outflow tract * unwillingness to participate in the trial

- requirement of therapy with nitrates of nitrites - arterial hypotension at presentation - recent diagnosis of coronary artery disease (<6 months) - acute heart failure at presentation - recent stroke (< 6 months) - chronic respiratory failure with co2 retention - known hypersensitivity to sildenafil - advanced liver disease (child-pugh class b or higher) - users of cytochrome p450 3a4 inhibitors (erythromycin, ketoconazole, itraconazole, saquinavir) - pulmonary hypertension - chronic users of phosphodiesterase 5 inhibitors - requirement of invasive mechanical ventilation at baseline - decision to limit therapeutic efforts at baseline - pregnancy or lactation - history of retinitis pigmentosa - known obstruction to left-ventricular outflow tract - unwillingness to participate in the trial

- requirement of therapy with nitrates of nitrites - arterial hypotension at presentation - recent diagnosis of coronary artery disease (<6 months) - acute heart failure at presentation - recent stroke (< 6 months) - chronic respiratory failure with co2 retention - known hypersensitivity to sildenafil - advanced liver disease (child-pugh class b or higher) - users of cytochrome p450 3a4 inhibitors (erythromycin, ketoconazole, itraconazole, saquinavir) - pulmonary hypertension - chronic users of phosphodiesterase 5 inhibitors - requirement of invasive mechanical ventilation at baseline - decision to limit therapeutic efforts at baseline - pregnancy or lactation - history of retinitis pigmentosa - known obstruction to left-ventricular outflow tract - unwillingness to participate in the trial