We found that echocardiography in cases of left juxtaposed atrial appendage (JAA) consistently featured a malpositioned right atrial appendage, abnormal spatial orientation of the atrial septum, and posterior deviation of the septum secundum toward the left atrium. The qualitative displacement of the septum secundum together with the posterior and leftward displacement of the right atrial appendage (with respect to the great arteries) prompted us to pose questions concerning the morphogenesis of left JAA and the implications for surgery. The importance of precatheterization and preoperative recognition of left JAA in dextrotransposition of the great arteries by echocardiography cannot be overemphasized when planning a balloon atrial septostomy or a biventricular repair.