Internal surface (left atrium, anatomy)

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