pulmonary vein

The pulmonary veins represent the venous return component of pulmonary circulation. After blood is oxygenated in the pulmonary capillaries surrounding the alveoli, it drains into progressively larger vessels: pulmonary venules → segmental pulmonary veins → lobar pulmonary veins → main pulmonary veins. The four main pulmonary veins (right upper, right lower, left upper, left lower) enter the posterior aspect of the left atrium. This completes the pulmonary circuit that began when the right ventricle ejected deoxygenated blood through the pulmonary arteries. Clinically, pulmonary veins are significant in several pathological conditions: they can be sites of ectopic electrical activity triggering atrial fibrillation (often targeted in pulmonary vein isolation procedures), they may develop stenosis following radiofrequency ablation, and they can be involved in rare conditions like pulmonary veno-occlusive disease. Anatomical variants include common ostia or supernumerary veins, which are important considerations during cardiac procedures.