Bronchogenic cysts are classified as congenital bronchopulmonary foregut malformations. It is very rare for bronchogenic cysts to occur within the heart. A 59-year-old woman had a cardiac mass which was detected incidentally during a CT examination. The lesion was a hypoechoic mass with internal echoes on transthoracic echocardiography, and a well-defined hyperdense mass within an interatrial septum with poor enhancement on electrocardiography (ECG)-gated cardiac CT. The lesion was diagnosed as a bronchogenic cyst in the interatrial septum after surgical excision.