Left Atrium

This close up image shows the left atrial appendage whith its typical pointed, acute angle apex and conspicuous scalloping and notching of its inferior border. A cephalad view of the fetal left and right atrial appendages shows diferences in the contours of the atrial appendage lumina.

Windows have been cut in the anterolateral walls of the left atrium and the left ventricle, leaving the mitral apparatus intact.
The smooth and thick endocardium of the atrium is shown in the atrial anterior wall and the atrial septum (AS). WIthin the atrial wall there are veins that open directly into the atrial chamber, these are called the Thebesian veins. The intimate contact of the anterior atrial wall with the pulmonary trunk and the root of the right (RPA) and left pulmonary arteries is shown. More anteriorly , and inferior to the right pulmonary artery trunk the left atrial appendage (LAA)is seen. The mitral chordal apparatus (MV) is easily seen.

A four chamber view section of the left atrium shows the smooth surface with thick endocardium.