Atrial septal defects are a common form of congenital heart disease that can present at any age, even in the elderly. As symptoms may be non-specific (breathlessness, palpitations), a high index of suspicion should be maintained. The ECG may be normal in the absence of significant pulmonary hypertension although a chest radiograph should be helpful. The diagnosis is usually confirmed by transthoracic echocardiography, although some types of atrial septal defects may be missed in adults who are poor echo subjects. Transoesophageal echo provides definitive diagnostic information and should be undertaken in any patient with right heart dilatation of unknown cause. Whilst closure of atrial septal defects may not prevent atrial arrhythmia, it can reduce the haemodynamic consequences if episodes occur. Many atrial septal defects can now be closed with percutaneous devices, avoiding the need for sternotomy.