internal surface (left atrium, anatomy)

Last reviewed 01/2018

The internal surface of the left atrium is notable for:

• its generally smooth endocardial surface; this is the result of most of the left atrium originating embryologically from the pulmonary veins
• the interatrial septum:
• passes obliquely, posteriorly from right to left across the cavity of the chamber
• often, a lunate depression is visible; this corresponds to the ostium secundum of the developing heart
• the narrow aperture leading to the auricle; as with the right atrial auricle, musculi pectinati line its surface; however, the ridges are less well developed than in the right atrium
• veins entering into the chamber:
• pulmonary veins, typically two on each side entering in the superior part of the chamber; there are no valves at the intersection of each vein with the chamber
• foramina venarum minimarum as in the right atrium
• the atrioventricular orifice:
• inferiorly and anteriorly within the chamber
• smaller than the right atrioventricular orifice
• associated with the mitral valve