Left atrium
The upper right chamber of the heart.
The left atrium receives oxygenated blood from the lungs and pumps it down into the left ventricle which delivers it to the body.</P> NTER><IMG height=423 alt='Atrial Fibrillation Illustration' src='http://images.medicinenet.com/images/illustrations/heartxsection.gif' width=489 border=0></CENTER>