may have Cushing's disease: get her tested ASAP
Sweetie, I really do feel for you because my lovely girl, Misty means the world to me, so I know how you must be feeling.
I have no knowledge of the heart problem, no experience of this. I wonder, if you asked your question on the Ask A Vet Expert Forum, you might get really good professional answers from the vets there.
There is no good time to have to say farewell to a good dog who is often closer to you than some humans. Even at age 19 it felt too soon, I know. But oh my gosh! How you must have loved and cared for that dog, like an angel. Because 19 is a very good old age for Mr Bones to pass away.
I wish your lovely little Cherry well. I will say a prayer for her, and hope that the medicines work well for her.