The Anatomy of the Left Coronary Artery

The left coronary artery supplies the left and back side of the heart

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The larger of the two coronary arteries, the left coronary artery emerges from the aorta and is a primary source of blood for the ventricles and left atrium of the heart. It moves to the left, coursing between the pulmonary trunk (which divides into the right and left pulmonary arteries that lead to the lungs) and left atrial appendage (a small sac in the muscle wall of the left atrium). After a short course, it terminates into the left anterior descending and circumflex arteries.

Given its location on the heart, disease or disorder of the left coronary artery can lead to serious health problems. Most notably, narrowing of this artery due to atherosclerosis can lead to coronary artery disease, which is extremely dangerous and can result in heart attack and failure.


Structure and Location

Originating from the aorta at the ostia (opening) of the left aortic cusp, the left coronary artery runs a short course across the front of the heart while dividing into the left anterior descending artery and the left circumflex artery. Usually about 4.5 mm in diameter and running only about 1 to 2 centimeters before dividing, it moves between the pulmonary trunk (connecting the heart to the lungs) and the left atrial appendage. This is where it starts to split into its two terminal branches:

  • Circumflex artery: This artery wraps around the heart, ensuring blood supply reaches the muscles on the backside of this organ.
  • Left anterior descending artery: Arising as a continuation of the left coronary artery, the left anterior descending artery moves downward, supplying the left ventricle and muscles in the front of the heart.

Anatomical Variations

The most common variation in the structure of the coronary arteries is an absent left coronary artery, observed in nearly 1 percent of people. In this case, the circumflex and left anterior descending arteries arise directly from the aorta. In addition, a number of other abnormalities can occur, including:

  • Varying branch origin: While the typical situation is that the circumflex and left anterior descending arteries arise from the left coronary artery at the same place, these may arise separately. In addition, doctors have observed the circumflex artery arising from the right coronary artery rather than the left.  
  • Varying coronary dominance: Dominance of one side over the other is determined by which artery system supplies the posterior descending artery, which supplies the backside of the heart as well as the interventricular septum (the thick wall that separates the heart’s ventricles, or lower chambers). The right coronary artery is dominant in about 80 percent of cases, the circumflex branch of the left coronary artery roughly 12 percent of the time, and in 6.2 percent of people, there is co-dominance.
  • Blood supply to the back of the heart: Differences have been observed in how the back walls of the heart are supplied. In some cases, more branches of the circumflex artery than usual are needed to bring necessary blood to these areas. Alternately, the left anterior descending branch of the left coronary artery wraps around the heart to access the backside of the organ.
  • Ramus intermedius: This variation involves the presence of an additional terminating branch of the left coronary artery (alongside the left circumflex and anterior descending arteries): the ramus intermedius. In these cases, this artery takes on the role of supplying the sides and back walls of the heart, especially when branches from the other two arteries are smaller or absent.
  • Myocardial bridging: Typically, a special layer of epicardial fat surrounds the coronary arteries, but in some cases, this is absent, and the arteries run directly through the muscular tissues of the heart (what’s called an “intramyocardial course”). Myocardial bridging is when this situation leads to compression of the vessel when the heart beats. This is most often is seen in the left anterior descending branch, though it can occur anywhere in the system.

Most of these aberrations are asymptomatic, but in some cases they can cause disruption of proper blood flow to the heart itself and lead to serious complications.

Despite being very uncommon, anatomical variations in the left coronary artery are the second leading cause of sudden cardiac arrest—when the heart stops working without warning—in young athletes.


The left coronary artery and its branches play a crucial role in ensuring that the muscles of the heart, itself, are supplied with oxygenated blood. Specifically, it provides the majority of supply to the ventricles (the lower chambers of the heart) as well as the left atrium and atrial appendage, the pulmonary artery, and aortic root. Naturally, these structures require a consistent source of oxygen and nutrients.

Clinical Significance

The central role that the left coronary artery plays in heart function means that disease or disorder of it or its branches can lead to very serious issues. Most notably, when the walls of the arteries narrow due to hardening and a build-up of plaques (atherosclerosis), the reduction in proper blood flow can lead to coronary artery disease. In these cases, and especially if the blockage becomes complete, the muscles of the heart don’t receive enough oxygen—a condition called ischemia. This can then lead to chest pains, heart attack, and, if untreated, sudden cardiac arrest.     

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