A 92-year-old man was referred to our hospital with decompensated heart failure. He was treated with diuretics and inotropic agents, but the clinical response was unsatisfactory. Echocardiography incidentally revealed an atrial septal defect (ASD) with a significant left-to-right shunt and pulmonary-to-systemic-blood-flow ratio of 2.36. Because the ASD was considered to be the primary cause of his treatment-resistant heart failure, the patient underwent transcatheter ASD closure. Shortly after shunt closure, his hemodynamics significantly improved, and he was discharged nine days later. This is an extremely rare case of a nonagenarian who showed an excellent clinical course after transcatheter ASD closure.