Left atrium
Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow.
Computer rendering of a human left atrium.
Latin	atrium sinistrum
Artery	circumflex branch of left coronary artery
Vein	oblique vein of the left atrium

The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the atrioventricular valve.

[edit] Foramen ovale

There is a foramen ovale (oval hole) between the right and left atrium in the fetus. After birth, this should close over and become the fossa ovale. If it does not, this is an atrial septal defect (hole in the heart). In the fetus, the right atrium pumps blood into the left atrium, bypassing the pulmonary circulation (which is useless in a fetus). In an adult, a septal defect would result in flow in the reverse direction - from the left atrium to the right - which will reduce cardiac output, potentially cause cardiac failure and in severe or untreated cases, death.

[edit] Blood supply

The left atrium is supplied mainly by the left circumflex coronary artery, though the branches are too small to be identified in a cadaveric human heart and are not named.

The oblique vein of the left atrium is partly responsible for venous drainage; it derives from the embryonic left superior vena cava.

[edit] Animals

Many other animals, including mammals, also have four-chambered hearts, and have a left atrium. The function in these animals is similar. Some animals (amphibians, reptiles) have a three-chambered heart, in which the blood from each atrium is mixed in the single ventricle before being pumped to the aorta. In these animals, the left atrium still serves the purpose of collecting blood from pulmonary veins.

[edit] Additional images

Heart seen from above.

Base and diaphragmatic surface of heart.

[edit] See also

• Right atrium