So very very sorry for your loss ...
We are seeing both ... rats with hugely enlarged hearts and badly damanged lungs so it is difficult to say which occurred first ... we try to treat both.
If rats with respir problems to not get better with various combos of respir. meds, then we try heart meds. So far all rats in those circumstances have responded to heart meds. If they respond to heart meds, then we try to treat both heart and lungs.
But no, you can't tell just from the breathing if it is the heart or the lungs that is the main problem.