Internal Anterior Section of the Sinus of the Pulmonary Veins

Description

Entering the left atrium, the paired right and left pulmonary veins open into a smooth posterior chamber whose internal surface contrasts with the pectinate muscle of the left atrial appendage, which lies anteriorly and laterally. An anterior section through the atrial wall would place the interatrial septum medially, with the region of the fossa ovalis nearby, while the mitral orifice sits inferior and anterior as the outflow toward the left ventricle. Superiorly, the atrial roof curves toward the pericardial reflection around the venous entries. Smooth wall. Clear margins. This sinus of the pulmonary veins (sinus venarum of the left atrium) matters because it is the anatomic substrate for pulmonary vein isolation in atrial fibrillation, where radiofrequency or cryoballoon lesions are placed around the venous ostia to electrically disconnect arrhythmogenic sleeves of atrial myocardium. An anterior internal section helps clarify why the pulmonary vein ostia are clustered on the posterior left atrial wall and why excessive posterior energy delivery risks injury to the esophagus, which lies immediately posterior to the left atrium. It also frames the surgical view used in mitral valve operations, where the left atrium is entered and the relationship between the mitral annulus and the posterior atrial wall guides exposure. Use this illustration in gross anatomy and cardiology teaching to distinguish the smooth left atrial wall from pectinate musculature, and in electrophysiology texts or patient education materials explaining catheter ablation around pulmonary veins and expected lesion geometry. It also suits operative atlases discussing left atriotomy planning and posterior left atrial landmarks during mitral valve repair. Anatomical accuracy verified by SciePro's Medical Advisory Board.