I hope for the best for you and your kitty! My sweet Theo has a heart murmur and I dread the day that he may go in to failure. Luckily we have some really good drugs to help these guys stay comfortable and happy (and eating!) once we can get the fluid off their chests. I also highly recommend echocardiogram if you have a facility nearby that can do it (or maybe your veterinarian can). It's invaluable in looking at the anatomical structure of the heart (x-rays only show us size and general shape) and a very good tool for making sure your kitty gets on the right drugs and you have an accurate prognosis.

T&P for Hunter from me & my kitty in west Texas.