The circumflex artery is a branch of the left coronary artery in the heart. Also known as the LCX, it is situated to the left atrium on the outside of the heart wall. This blood vessel branches off the left coronary artery on the top left side of the heart. The coronary artery arises from the aorta, the major artery exiting the heart to deliver oxygenated blood to the rest of the body. The function of the circumflex artery is to distribute oxygenated blood to the left ventricle of the heart and to supply blood to the papillary muscles, the pumping muscles of the heart, on the front outer side of the left ventricle.
To understand the role of this artery, it is helpful to understand the basic function of the circulatory system, which includes the heart, lungs, and blood vessels. During respiration, or breathing, air is drawn into the lungs, which take up oxygen from the air. The pulmonary artery brings deoxygenated blood from the right ventricle of the heart to the lungs, where this oxygen is transferred to the blood and circulated via red blood cells out through the pulmonary veins and back into the heart via the left atrium. It is then pumped down through the left ventricle and out of the heart through the aorta, which then transports this oxygen and nutrient-rich blood out to the body. Once that blood has been depleted of its oxygen by distribution to various tissues, it is returned to the heart by veins like the vena cava and deposited into the right atrium, from which it is pumped into the right ventricle so that the cycle can begin again.
When this oxygenated blood leaves the heart via the aorta, a portion of it enters the coronary artery and makes its way into the circumflex artery. This blood vessel is distinctive in that it supplies the heart itself with oxygen and other nutrients the muscle requires to properly function, such as glucose, which the heart muscle requires for energy to keep the heart pumping. The circumflex artery delivers these nutrients by way of the left marginal artery, the posterolateral artery, and the left atrial branch.
After the circumflex artery courses downward around the outside of the heart within a groove known as the coronary sulcus, which divides the atria from the ventricles, it branches into smaller tributaries. Two of these, the left marginal artery and posterolateral artery, supply blood to the left ventricle and the papillary muscles, muscles inside the heart that perform the pumping action. An additional smaller portion of the blood from the circumflex artery goes to the left atrial branch of the right coronary artery, which brings blood to the right and left atria.