You might want to order a copy of Debbie Ducommun's Rat Health Care booklet, which talks about the diagnosis and care of heart problems in rats.
I have had a couple of rats with heart problems. sometimes you notice first that they get out of breath with normal exertion, e.g. after going up a ramp. Sometimes you hear noisy breathing, especially after they've eaten. Sometimes they get frequent respiratory problems for which antibiotics might help a bit at first, yet the problems recur.
The vet can diagnose sometimes with an X-ray. If the heart is enlarged and s/he hears fluid on the lungs, that makes it likely. If treatment with Lasix and an ACE-inhibitor helps, then it is probably congestive heart failure (CHF). If the heart is enlarged the vet may prescribe a beta-blocker to lower blood pressure and maybe Digoxin to help the heart beat more strongly. Debbie D's book says not to do that if the heart is normal size with thickened walls, but you would need an echocardiogram to determine that. I imagine that is difficult to get.
Debbie D says that some of her rats with CHF have lived for a long time. I have not been so lucky, but I was learning with the first rat and may not have done things soon enough or actively enough. My last rat with CHF did well for eight months, then went downhill rapidly. It seemed as if the heart had been overtaxed and then suddenly couldn't function. Another thing I have been concerned with is the expiry of compounded medications. Nobody knows exactly how long they last after mixing. They assume 3 months, but one article I found said one month. I often wonder whether that is why Georgie would do well for a while and then have several bad days. I will track things carefully next time.
Hope this helps. I am no expert, and I wish I had known more with my first ratty.
