We investigated the short-term and medium-term results in patients with pulmonary arterial hypertension (PAH) associated with atrial septal defect (ASD) undergoing transcatheter closure. Fifteen patients with severe PAH associated with ASD who underwent successful occluder implantation from 2007 to 2010 were included. Clinical, echocardiographic, and hemodynamic data were reviewed. Severe PAH was defined as pulmonary arterial systolic pressure measured by catheterization was ≥60 mmHg and pulmonary vascular resistance (PVR) ≥6 Wood Units (WU). Compared with baseline, the 6-minwalking distance significantly increased by 29.7 ± 26.3 m (P < 0.001) at 3 months (short-term) and 65.4 ± 63.6 m (P < 0.001) at 23.4 ± 9.7 months (medium-term), World Health Organization function class considerably improved after postclosure short-term and medium-term. Repeat cardiac catheterization (n = 7) showed that mean pulmonary arterial pressure decreased from 51.6 ± 9.4 mmHg at baseline to 21.0 ± 3.8 mmHg (P < 0.001) at follow-up of 12 months. The PVR decreased by 5.6 ± 1.1 WU (P < 0.001). Through carefully selected patients with severe PAH associated with ASD, transcatheter closure can be safely performed with a promising short-term and medium-term outcome. Trial occlusion is an effective way for deciding the reversibility of severe PAH in ASD patients. The role of aerosolized iloprost for pulmonary vasoreactivity testing in patients with severe PAH secondary to ASD requires further investigation.