A 45-year-old woman was admitted to our cardiology department for palpitations and dyspnoea. She had previously been investigated by echocardiography several times, resulting in a diagnosis of hypertrophic cardiomyopathy. However, a congenitally corrected transposition of the great arteries was diagnosed by our echocardiographic examination. The patient underwent electrophysiological evaluation and the accessory pathway was successfully ablated by applying radiofrequency pulses. This case report identifies that in patients with congenitally corrected transposition of the great arteries the primary diagnosis by echocardiography can sometimes be missed and that these patients are increasingly liable to develop Congestive Heart Failure with advancing age. In order to avoid diagnostic mistakes, more widespread dissemination of information about this congenital heart defect is essential.