An ostium (pl. ostia) is a generic medical term for "hole" - for example, there are coronary ostia in the aorta through which blood flows to the coronary arteries. Most people are born with two coronary ostia, one each for the left coronary artery and the right coronary artery.
Variations in normal aortic root anatomy can vary the locations of the coronary ostia, such as having both ostia on one side or having extra branches off of the main coronary arteries, however, in rare cases, the number of openings can also vary. A single, third, or fourth (or even fifth) coronary ostium can exist as congenital anomalies. Most often, this type of congenital heart defect is discovered soon after birth because of circulation and oxygenation problems, but some patients will live into adulthood, undetected, with no symptoms. When pathological, these anomalies can disrupt or cause ineffective blood flow, creating a site for clot formation or the growth of an infection. In such cases, there is high risk for embolism, infarction, and sudden death. Treatment usually involves closing the ostium with surgery.