The left atrium (LA) is one of the chambers of the heart located in the superior left corner above the left ventricle (LV), opposite to the right atrium (RA). The pulmonary circulation ends in the left atrium, as oxygenated blood from the lungs enter it through the pulmonary veins.

The left atrium has a cuboid shape, it is thicker, but smaller in the volume than the right atrium.

There are five openings found in the walls of the LA, and these include:

Four openings for the pulmonary veins - located on the superior and posterior walls. The pulmonary veins carry oxygenated blood from the lungs to the left atrium;
Left atrioventricular orifice - on the inferior wall of the left atrium and carries oxygenated blood to the left ventricle. Around the left atrioventricular orifice is the mitral valve (also known as bicuspidal valve).

The medial wall of the left atrium is formed by the interatrial septum, which separates the left and right atrium.

On the anterior surface of the left atrium lies the left auricle (or left atrial appendage), a flap of the heart wall. The left auricle has an irregular shape with many tiny ridges created by the pectinate muscles. Elsewhere, the inner surface of the left atrium is smooth. The main function of the left auricle is to increase the volume of the left atrium.

Unlock with Premium

Left atrium (LA)