The internal thoracic artery originates from the first part of the subclavian artery, branching off its front-facing (anteroinferior) surface. It arises directly below the thyrocervical trunk, roughly one finger-width to the side of the joint where your collarbone meets your breastbone. From there, it descends along the inner surface of the front chest wall, supplying blood to structures from the chest down to the upper abdomen.
Origin From the Subclavian Artery
The subclavian artery is divided into three parts based on its relationship to a neck muscle called the anterior scalene. The internal thoracic artery branches off the first part, which is the segment closest to the center of the body. It sits opposite the thyrocervical trunk, a short arterial trunk that sends branches to the neck and shoulder region. This close pairing of two major branches in the same small area is a consistent anatomical landmark surgeons rely on.
Anatomic variants do exist. The most common variation is an anomalous origin, where the artery arises from a different segment of the subclavian artery, from one of the subclavian’s own branches, or as a shared trunk with the thyrocervical trunk. These variants are uncommon but clinically relevant during chest surgery or imaging.
Course Through the Chest Wall
After branching off the subclavian, the internal thoracic artery descends along the inside of the anterior chest wall, running about two to three centimeters to either side of the breastbone (sternum). That puts it slightly medial to the nipple. It travels sandwiched between two muscle layers: the transversus thoracis muscle behind it and the internal intercostal muscles and costal cartilages in front of it. It sits beneath the fascia and deep to the intercostal muscles, so it’s not palpable from outside.
As it descends, it gives off small branches at each intercostal space. These anterior intercostal arteries supply the front portions of the spaces between the ribs, while perforating branches pass through to supply skin and superficial tissue of the chest. In women, some of these perforating branches provide blood supply to the breast.
The phrenic nerve, which controls the diaphragm, crosses the internal thoracic artery near its origin. In about 54% of people, both phrenic nerves cross in front of the artery. In 14%, both cross behind it. The remaining cases show mixed patterns, with the right and left nerves taking different routes. This variable relationship matters during thoracic surgery, where accidental injury to the phrenic nerve can impair breathing.
Terminal Branches
At the level of the sixth or seventh costal cartilage, the internal thoracic artery splits into its two terminal branches: the musculophrenic artery and the superior epigastric artery. The musculophrenic artery curves along the inner surface of the lower ribcage and helps supply the diaphragm and lower intercostal spaces. The superior epigastric artery continues downward, crossing the diaphragm and entering the abdominal wall.
The superior epigastric artery runs between the abdominal muscles and the tissue sheath covering them, feeding the rectus abdominis (the “six-pack” muscle) as it descends. Around the level of the belly button, it connects with the inferior epigastric artery, which rises from the external iliac artery in the pelvis. This connection creates a continuous arterial pathway from the subclavian artery above to the external iliac below, forming a critical collateral route. If blood flow through the aorta is ever compromised, this chain of arteries can serve as a bypass to keep blood moving between the upper and lower body.
Why It Matters in Heart Surgery
The internal thoracic artery is sometimes called the internal mammary artery, and you’ll often see it referred to as the LIMA (left internal mammary artery) or RIMA (right) in the context of coronary artery bypass grafting (CABG). Surgeons favor it as a bypass graft because its wall structure resists the buildup of plaque far better than vein grafts do.
The numbers reflect that advantage. A study published in the Journal of Thoracic Disease found that left internal thoracic artery grafts had patency rates of 96% at one year, 96% at five years, and 93% at ten years when connected to severely narrowed coronary arteries. Right internal thoracic artery grafts performed slightly lower, at 91%, 87%, and 80% over the same intervals. These long-term results are a major reason the left internal thoracic artery graft to the left anterior descending coronary artery has become the gold standard in bypass surgery.
Because of its surgical importance, the artery’s precise origin, course, and any anatomic variants are carefully mapped during preoperative imaging. Knowing exactly where it branches from the subclavian and how it runs along the chest wall allows surgeons to harvest it with minimal damage to surrounding tissue.