In 85% of people, the posterior descending artery arises from the right coronary artery (RCA) in the posterior interventricular groove ('right dominance').

In 15% of people, the posterior descending artery arises from the circumflex artery in the posterior interventricular groove ('left dominance').

Fig 1 shows a labelled, right coronary angiogram

Fig 2 shows a labelled, left coronary angiogram