The left coronary artery, also abbreviated LCA, arises from the aorta above the left cusp of the aortic valve. It typically runs for 1 to 25 mm and then bifurcates into the left anterior descending (LAD) artery and the left circumflex artery (LCX). The part that is between the aorta and the bifurcation only is known as the left main artery (LM), while the term 'LCA' might refer to just the left main, or to the left main and all its eventual branches. If an artery arises from the left main between the LAD and LCX, it is known as the ramus intermedius. The ramus intermedius occurs in 37% of the general population, and is considered a normal variant.

The LAD runs down the anterior interventricular groove, and is known as the anterior interventricular artery in anatomy texts. In 78% of cases, it reaches the apex of the heart. It supplies the anterolateral myocardium, apex, and interventricular septum. The LAD typically supplies 45-55% of the left ventricle (LV). The LAD gives off two types of branches: septals and diagonals. Septals originate from the LAD at 90 degrees to the surface of the heart, perforating and supplying the intraventricular septum. Diagonals run along the surface of the heart and supply the lateral wall of the LV and the anterolateral papillary muscle.

The LCX runs across the left atrioventricular groove. It gives off obtuse marginal (OM) branches. The LCX supplies the posterolateral LV and the anterolateral papillary muscle. It also supplies the sinoatrial nodal artery in 38% of people. It supplies 15-25% of the left ventricle in right-dominant systems. If the coronary anatomy is left-dominant, the LCX supplies 40-50% of the left ventricle. (See Coronary circulation for description of dominance.)

See also

• Coronary circulation