Although I'm sure the dynamic attending is a wonderful human being and may happily name a child after you some day, the prominent cardiologist will be recognized by more eyes. More cache means more attention. Hopefully the glamorous cardiologist actually knows you. If s/he isn't really familiar with you, a general (blah) LOR won't pack a huge punch.
But here's another idea if you absolutely can't decide. We've had candidates upload more than three letters. Granted, you'll have to cancel one out in ERAS, but we can see all of them and have total access to all of them. The one you cancel out will show a little red X next to it in our pull-down menu, but the letter is there all the same. Don't cancel the PD's LOR.
I'm not encouraging anyone to go crazy and upload more than four LORs (PD LOR + three from cardiologists). Like it or not, a ton of letters is overkill and off-putting.