Posterior interventricular a.

The posterior interventricular artery (PIV) or posterior descending artery (PDA) is an artery running in the posterior interventricular groove to the apex of the heart, where it meets with the anterior interventricular (left anterior descending) artery. It supplies the posterior 1/3rd of the interventricular septum. The remaining anterior 2/3rds is supplied by the anterior interventricular artery, one of the two main branches of the left  coronary artery.

The PIV is typically a branch of the right coronary artery (85%, known as Right Dominance). Alternately, the PIV can be a branch of the circumflex coronary artery (15%, known as Left Dominance), the other of the two main branches of the left coronary artery.