Opening of left inferior pulmonary vein

The opening of the left inferior pulmonary vein refers to the ostium (or orifice) where the left inferior pulmonary vein enters the left atrium of the heart.

In typical anatomy, the left inferior pulmonary vein is one of four pulmonary veins that drain oxygenated blood from the lungs into the left atrium. The ostium has a mean diameter of approximately 13.3 ± 3.4 mm in adults with the classical four-vein pattern. The opening is located on the posterolateral wall of the left atrium, positioned inferior to the left superior pulmonary vein ostium. 

The anatomical definition of the ostium is typically determined by the outer contour of the left atrium—if the pulmonary vein enters the left atrium separately outside this boundary line, it is defined as having a "separate ostium". However, in approximately 4-5% of cases, the left superior and inferior pulmonary veins may share a common ostium, where they unite before entering the left atrium. The mean distance from the ostium to the last tributary (closest to the atrium) is approximately 13.5 ± 4.0 mm for the left inferior pulmonary vein.