Sildenafil (Viagra, Pfizer) is being used to treat pulmonary hypertension (PH). However, there are limited data on the effects of sildenafil on patients with PH after left-sided valvular surgery. The purpose of this study was to determine the optimal dosage and the effects of sildenafil on prognosis of patients with PH after left-sided valvular surgery.This randomised controlled trial, double-blind study enrolled patients with PH undergoing left-sided valvular surgery in our hospital from January to December, 2010. Ninety patients were enrolled. And 0.5mg/kg sildenafil citrate or placebo was administered through nasogastric tubes, the haemodynamics changes in the 0.5/1/2/4hours were assessed. The sildenafil citrate/placebo was continued to the discharges and the early prognoses of these patients were compared.Compared with placebo, a 0.5mg/kg dose of sildenafil significantly reduced the time of mechanical ventilation, stay-in-ICU and hospitalisation duration.Sildenafil might be beneficial to the early prognosis of patients with PH after left-sided valvular surgery.