The atrial septal defect (ASD) is the most commonly diagnosed congenital defect in adults and has a prevalence of 7.5% of all congenital cardiac anomalies. Less invasive imaging techniques, especially transthoracic and transoesophageal echocardiography, provide more accurate diagnostics, resulting in earlier diagnosis and treatment. Despite these opportunities in high-tech countries, medicine may still fail in detecting initially correctable cardiac anomalies. We present a case of 41-year-old woman with an abnormal murmur at childhood that disappeared with time due to the development of an Eisenmenger syndrome. The importance of a complete haemodynamic evaluation in this patient is illustrated.