An adult case of single atrium diagnosed using three-dimensional echocardiography

Previously, complete absence of an interatrial septum (IAS) was thought to be a form of an atrioventricular septal defect involving the cleft mitral valve and interventricular communication. Ellis et al. (1) defined this condition as common atrium (CA). This congenital cardiac anomaly is especially observed in association with heterotaxy syndrome. Levy et al. (2) reported a case of complete absence of IAS without other cardiac defects; however, this condition was different from CA defined by Ellis et al. (1). They used the term single atrium (SA) to denote this anomaly.