The internal thoracic artery (ITA), also known as the internal mammary artery, is an artery that supplies the anterior chest wall and the breasts. It is a paired artery, with one running along each side of the sternum, to continue after its bifurcation as the superior epigastric and musculophrenic arteries.

The internal thoracic artery arises from the anterior surface of the subclavian artery near its origin. It has a width of between 1-2 mm.

It travels downward on the inside of the rib cage, approximately 1 cm from the sides of the sternum, and thus medial to the nipple. It is accompanied by the internal thoracic vein.

It runs deep to the abdominal external oblique muscle, but superficial to the vagus nerve.

In adults, the internal thoracic artery lies closest to the sternum at the first intercostal space. The gap between the artery and lateral border of the sternum increases when going downwards, up to 1.1 cm to 1.3 cm at the sixth intercostal space. In children, the gap ranges from 0.5 cm to 1.0 cm.

After passing the sixth intercostal space, the internal thoracic artery splits into the following two terminal branches:

The internal thoracic artery supplies the chest wall and the breasts.

The internal thoracic artery is the cardiac surgeon's blood vessel of choice for coronary artery bypass grafting. The left ITA has a superior long-term patency to saphenous vein grafts and other arterial grafts (e.g. radial artery, gastroepiploic artery) when grafted to the left anterior descending coronary artery, generally the most important vessel, clinically, to revascularize.