A 32-year-old man underwent excision of an aneurysm of the left atrial appendage which had been causing palpitation and supraventricular tachyarrhythmia. Various techniques are useful for making the diagnosis and allowing differential diagnosis between this and other pathologies. In this report, the diagnosis was based on transthoracic and transesophageal echocardiography, and the patient was treated by surgical resection of the aneurysm on cardiopulmonary bypass. There were no postoperative complications. Four months later, the patient remained asymptomatic and in sinus rhythm.