We investigated the mid-to-long-term results of transcatheter closure of atrial septal defect (ASD) in patients >= 40 years since there are issues with patients presenting with pulmonary hypertension and arrhythmia at the time of closure. In an 8.8 year period, transcatheter closure of ASD was successful in 179 patients aged >= 40 years, but failed in 2. Of the 179 patients (44 males, median 53 years), NYHA functional class, presence of arrhythmia and severity of pulmonary hypertension were compared before and after closure. Patients with pulmonary hypertension (n = 43, 24 %) were significantly older (60 +/- 11 vs. 52 +/- 9 years, p < 0.01) and required larger devices (27 +/- 7 vs. 24 +/- 7 mm, p = 0.04) than those without. Arrhythmia before intervention was documented in 31 patients (17.3 %): 22 atrial fibrillation (AF), 4 atrial flutter and 5 supraventricular tachycardia. Patients with AF or atrial flutter (n = 26) were significantly older (63 +/- 10 vs. 53 +/- 10 years, p = 0.048) and had a higher pulmonary artery mean pressure (29.2 +/- 12.6 vs. 20.2 +/- 7.6 mmHg, p = 0.041) than those without. The mean follow-up period was 3.8 +/- 2.1 years. Early new-onset arrhythmia was documented in 23 patients of whom 1 had persistent AF, 1 developed sick sinus syndrome and others were in sinus rhythm at latest visit. There was significant improvement in NYHA functional class after closure (p < 0.001). Of the 22 patients with AF, 10 were in sinus rhythm, 1 had paroxysmal AF, and 11 had persistent AF. Pulmonary hypertension persisted in 13 patients. Transcatheter closure of atrial septal defect in patients above 40 years is beneficial in terms of NYHA functional class, pulmonary artery pressure and cardiac rhythm.