Ramus intermedius artery

The ramus intermedius is a variant coronary artery resulting from trifurcation of the left main coronary artery ¹. It is present in ~20% (range 15-30%) ^2-3,3 of the population.

It can have a course similar to the obtuse marginal branches of the left circumflex artery or the diagonal branches of the left anterior descending artery and thus can supply either the anterior or medial aspect of the heart ¹. 

The peculiarity of this vessel is that it does not run along an anatomical groove and imply simply slides over the free surface of left ventricle instead.

Practical points

In practice, even if there is not a true trifurcation, some cardiologists may term a prominent early branching (high origin) obtuse marginal artery a ramus branch if it supplies the territory of small diagonal branches since there is an inverse relationship between the size of the ramus intermedius and the size and distribution of the diagonal branches.