Background Although sildenafil has been shown to be safe and effective in idiopathic pulmonary arterial hypertension (PAH) and PAH related to connective tissue disease, its effects in Eisenmenger syndrome are less clear.

Objective To investigate whether long-term treatment (12 months) with the phosphodiesterase type 5 inhibitor sildenafil improves clinical and haemodynamic parameters in patients with Eisenmenger syndrome.

Design Prospective, open-label, multicentre study.

Setting Four pulmonary hypertension centres in China.

Patients 84 Eisenmenger syndrome functional class II–IV patients.

Interventions Oral sildenafil 20 mg orally three times a day.

Outcome measures 6-min walk distance (6MWD) test, resting systemic arterial blood oxygen saturation (SaO₂) in room air, haemodynamic parameters assessed by right heart catheterisation, safety and tolerability.

Results The overall treatment effects at 12 months versus baseline (mean changes with 95% CIs) were 56 m increase (42 to 69, p<0.0001) in 6MWD, and 2.4% increase (1.8% to 2.9%, p<0.0001) in resting room air SaO₂. Improvements were also seen in mean pulmonary arterial pressure and pulmonary vascular resistance index (−4.7 mm Hg (−7.5 to −1.9), p=0.001; and −474 dyn×s×cm⁻⁵×m² (−634 to −314), p<0.0001, respectively). Sildenafil was well tolerated. Most adverse events were mild and transient, and occurred in the first 2 weeks of treatment.

Conclusions Twelve months of oral sildenafil treatment was well tolerated and appeared to improve exercise capacity, systemic arterial oxygen saturation and haemodynamic parameters in patients with Eisenmenger syndrome.