Editing Coronary circulation (section)

===Variation===
The left and right coronary arteries occasionally arise by a common trunk, or their number may be increased to three; the additional branch being the posterior coronary artery (which is smaller in size). In rare cases, a person will have the third coronary artery run around the root of the aorta.{{citation needed|date=April 2021}}

Occasionally, a coronary artery will exist as a double structure (i.e. there are two arteries, parallel to each other, where ordinarily there would be one).{{citation needed|date=April 2021}}

====Coronary artery dominance====
The artery that supplies the posterior third of the [[interventricular septum]] – the [[posterior descending artery]] (PDA)<ref>{{Chorus|00460}}</ref> determines the coronary dominance.<ref name="Hurst">{{cite book | last=Fuster | first=V |author2=Alexander RW|author3=O'Rourke RA | title=Hurst's The Heart | publisher=McGraw-Hill | year=2001 | page=53 | edition=10th | isbn=0-07-135694-0 }}</ref>
* If the posterior descending artery is supplied by the [[right coronary artery]] (RCA), then the coronary circulation can be classified as "right-dominant."
* If the posterior descending artery is supplied by the [[circumflex branch of left coronary artery|circumflex artery]] (CX), a branch of the left artery, then the coronary circulation can be classified as "left-dominant."
* If the posterior descending artery is supplied by both the right coronary artery and the circumflex artery, then the coronary circulation can be classified as "co-dominant."

Approximately 70% of the general population are right-dominant, 20% are co-dominant, and 10% are left-dominant.<ref name="Hurst"/>
A precise anatomic definition of dominance would be the artery which gives off supply to the AV node i.e. the AV nodal artery. Most of the time this is the right coronary artery.{{citation needed|date=April 2021}}