The left atrial appendage (LAA) is a small, pouch-like structure in the left atrium of the heart. The LAA acts as a contractile reservoir and a decompression chamber.

In normal hearts, the LAA plays a role in regulating blood volume by storing and releasing hormones called atrial natriuretic peptides. It produces approximately 30% of ANPs, which are released in response to stretch, helping regulate blood volume and pressure. Due to its anatomical position and greater ability to swell compared to the main left atrium, it can act as a decompression chamber during periods of increased left atrial pressure, thereby reducing stress on the atrial walls.

As a contractile reservoir, it aids the movement of blood from the left atrium to the left ventricle. During atrial systole, the LAA empties into the left ventricle and assists with filling the left ventricle during late diastole. This contraction helps prevent blood from pooling and stagnating, which leads to the formation of blood clots.

(Naksuk et al., 2016)