If there's a vet cardiologist in your area, would it make sense to have a thorough exam and test, just so you know exactly what's going on? At the moment this is speculation based on a lot of knowledge, and intuition. A cardiologist might want to do an utra-sound test to see exactly what's going on. Then you'd, hopefully , know what it is you're dealing with. But cardiologists are not easy to find. Our area only recently acquired one.