The left main coronary artery (LMCA) arises from the left aortic sinus, running towards the left hand side of the heart, just below the left auricle. It quickly divides into the anterior interventricular branch also known as the left anterior descending (LAD) artery and the circumflex artery.The LAD runs along the anterior interventricular sulcus, a groove in the anterior surface of the heart that seperates the left and right ventricle, down towards the apex.rom here, it curls around towards the inferior surface of the heart, forming the posterior interventricular branch, more commonly known as the posterior descending artery (PDA). The PDA runs along the posterior interventiculas sulcus, to supply blood to the walls of both the left and right ventricle.