Atrial auricle

An atrial auricle is a small, ear-shaped muscular pouch that projects from the main body of each atrium of the heart; it is also referred to as the atrial appendage. The left atrial auricle (left atrial appendage, LAA) and right atrial auricle (right atrial appendage, RAA) are morphologically distinct structures that arise embryologically from the primitive atrium and are characterized by a trabeculated endocardial surface due to pectinate muscles, in contrast to the smoother walls of the atrial body.