The left pulmonary artery (LPA) is one of the branches of the pulmonary trunk, branching at the level of the transthoracic plane of Ludwig. It is shorter than the right pulmonary artery and represents a direct posterior continuation of the pulmonary trunk. It arches posterosuperiorly over the superior margin of the left main bronchus and when posterior to the bronchus enters the superior aspect of the hilum of the left lung where it divides.

The branching pattern is variable, much more so than that of the right pulmonary artery. In >90% of cases, there are 3-5 branches of the left pulmonary artery that vascularize the left upper lobe in various configurations ⁴.

The part supplying the left lower lobe may be called the descending or interlobar artery. In most cases, one or two branches are given off supplying the apical segment before splitting into two terminal divisions ⁵.

In the fetus, the ductus arteriosus connects the proximal left pulmonary artery to the undersurface of the isthmus of the aorta, allowing blood to bypass the lungs. At birth, the ductus closes, and over time fibroses to form the ligamentum arteriosum, which may calcify.