Lunules of the Pulmonary Valve Semilunar Leaflet in Transverse Heart Section

Description

Cut through in transverse section, the right ventricular outflow tract (infundibulum) leads anterosuperiorly into the pulmonary trunk, where the pulmonary valve sits at the ventriculoarterial junction. Along the free edge of a pulmonary valve semilunar leaflet, the lunules form thin crescentic zones that extend from each commissure toward the midline nodule (nodule of Arantius), the coaptation surface facing centrally into the valve orifice. Posterior to this complex lie the left atrium and pulmonary veins, while the interventricular septum remains medial to the right ventricular cavity and the left ventricular outflow tract lies more posterior and leftward. Lunules matter because they are the tissue that actually meets during valve closure, and a small defect or retraction along this crescent can produce pulmonic regurgitation even when the leaflet body looks intact. Congenital pulmonary valve stenosis and dysplastic valve morphology alter commissural alignment and leaflet coaptation, and this view makes it easier to teach why post-stenotic dilation of the pulmonary trunk can coexist with an apparently thickened but still incompetent valve. Surgeons and imagers also use the lunules and nodules as orientation points when correlating gross anatomy with short-axis echocardiographic or CT planes through the semilunar valves. Small details. Big consequences. Cardiac anatomy instructors can place this figure directly into teaching on semilunar valve mechanics, contrasting the pulmonary valve with the aortic valve in transverse heart sections and explaining why right-sided murmurs change with respiration. It also suits congenital heart disease chapters, valve pathology atlases, and operative planning discussions where precise commissural and coaptation anatomy guides repair versus replacement. Anatomical accuracy verified by SciePro's Medical Advisory Board.