The Circumflex (Circ) coronary artery is a branch of the left main coronary artery. It travels in the left atrio-ventricular groove that separates the left atrium from the left ventricle. The Circ moves away from the LAD and wraps around to the back of the heart. The major branches that it gives off in the proximal or initial portion are known as obtuse (pronounced Ob-tews) marginal or OM coronary arteries. As it makes its way to the back or posterior portion of the heart, it gives off one or more left postero-lateral (PL) branches.

   In 85% of cases, the Circ terminates at this point and is known as a non-dominant left coronary artery system. In the other 15% of cases, a dominant Circ supplies the PDA or posterior descending artery, which run in the bottom of the heart within a groove that separates the left from the right ventricle.