Coronary Ostial Stenosis or Atresia (COSA) is a spectrum of rare developmental conditions with different implications in pathophysiologic mechanisms and clinical areas. A normal coronary ostium is located in the middle of aortic sinus. However, when the left ostium is located at sinus of Valsalva that is abnormal for distal coronary distribution, the situation is that one of the anomalous coronary artery origin from the opposite sinus with intramural course (ACAOS).

What does it mean in layman understanding ? In simple words, that means one of the coronary artery is crossing/taking direction off the ostium, passing off to the correct side of the heart & lying within the aortic wall. There are various conditions & complications to Coronary Ostial Stenosis or Atresia (COSA). Each of these could considered as subclass of Congenital Coronary Artery Anomalies (CAAs). On the fundamental distinction between COSA and related condition, it involves the particular ectopic origin of coronary artery, from the other opposite coronary artery.

In mose, Coronary Ostial Stenosis or Atresia would affects Left Ceronary Artery (L-COSA) more than the Right Coronary Artery (R-COSA). Origin of the Left Main Coronary Artery from the right aortic sinus is clinically important, although it is uncommon.

In some clinical adult patients cases, it could be much difficult to determine whether coronary defect has been present since birth. Further, it might not be recognized until later in time, as to whether it is total or partial-obstruction COSA. By then, whether it is mild or nonexistent functional stenosis at birthtime, might have become much severe.