ABSTRACT
PURPOSE--To study the spatial arrangement of the bundles of myocardial fibers presents in the left atrial-venous junctions and in the wall of the pulmonary veins. METHODS--The study was made on 24 human adult hearts, together with pulmonary vessels, fixed in 10 per cent formaldehyde solution. Each specimen was cleared of remnants of pericardium to expose the myocardial fibers as clearly as possible. Particular attention was paid to the atrial-venous junction and the extension of the myocardial fibers in the pulmonary veins. The specimens were embedded in celloidin and cut serially at a thickness of 70 mu and stained by methods of Azan's trichrome. RESULTS--The myocardial bundles leave the atrial wall around the openings of all pulmonary veins forming a sphincter-like structure. These fibers are continuous in the adventitial coat running in oblique or spiral directions. Some bundles, more external, leaving from the atrial wall, surround the ostium of the veins and return to the atrium, forming true loops. CONCLUSION--The extremities of the pulmonary veins and their junctions with the atrium have a morphological substract which may be of physiological importance in the control of the pulmonary venous pressure and blood flow