The walls of the left atrium are slightly thicker than the walls of the right atrium. Oxygen-rich blood from the lungs enters the left atrium through the pulmonary vein.

Electrogram recordings in a patient with a focal pulmonary vein (PV) tachycardia originating from the right upper PV (RUPV). The fluoroscopic image (left anterior oblique projection) in (A) shows ...