100% of 3 Pros
I am not an interventional radiologist, however in the places I have worked, it seems to vary and depend on the interest in collaboration between the two departments. There can be very close collaboration between the two, if both are interested.
These two specialties are actually very different, although they have some shared procedures. My advice would be to shadow both specialties in clinic and see what fits your personality best. The training that cardiologists go through (3 years of IM and 3 years of cards) is vastly different from radiology training (5 years radiology and 1-2 years of interventional).
I am an interventional radiologist. Because of the overlap in treating peripheral vascular disease, DVT, and PE, interventional radiologists and cardiologists are more competitors rather than collaborators.