The left atrial appendage is a structure of the left atrium that is a dilation around the four pulmonary veins (the right superior vein and upper left vein and the right inferior and left inferior vein).
Its function is to avoid the stagnation of blood in the corresponding atria because they are described internally as sack bottoms formed by pectinate second and third order cardiac muscles. Nomenclature
Note that the term in English and Latin "auricula" is a false friend that should not be translated as "auricle", but as "appendage". For this reason, the Anatomical Terminology gives p to the term "atrium" to define what is traditionally known as "atrium".
wiki
