Coronary artery. Coloured X-ray angiogram of a healthy heart showing the branching left coronary artery (blue). The left and right coronary arteries supply blood to the heart muscle. The left coronary artery branches to form the anterior interventricular artery, which supplies blood to the anterior walls of both the heart ventricles (lower chambers) and the interventricular septum, which divides the ventricles. The other branch of the left coronary artery, the circumflex artery, supplies the left atrium (upper heart chamber) and the posterior walls of both ventricles. X-ray angiography injects a radio-opaque contrast medium to highlight blood vessels.