This document discusses the anatomy and classification of atrial appendages. It notes that there are normally two atrial appendages, a right and left, which can be classified in two ways. Rarely, both atrial appendages may be juxtaposed on the same side of the heart in conditions like transposition of the great arteries or tricuspid atresia. When this occurs, the left atrial appendage is juxtaposed about three times more often than the right. Having both appendages on the right side is generally associated with more cardiac issues than when both are on the left.