Cooper's HCM Developed Quickly-Believe Weight Loss Last Summer Indicated Onset

Did I mention Cooper's HCM developed quickly? He had an echo two years ago when he first had hypercalcemia and we were worried about the effects on the heart. The echo was clear. He had a stress related murmur that he's had even as a kitten but no sign of disease. Last summer he weighed 12.8 lbs and began to slowly lose weight-an ounce here, 1/2 ounce there but he was eating well enough. By December he wasn't always eating everything offered and by the end of December he weighed 12.1 lbs. We knew that he hadn't been eating well but thought it had to do with the tooth he was losing to resorption. Two months later at the dental surgery, he weighed 11.5. We had not realized that he had drastically lost weight. We now believe the weight loss indicated the onset of heart disease. At no time did he ever present with congestion until last week. It wasn't until he really didn't want to eat last week, and that he looked tired, and that on Thursday seemed to breathe fast, that I knew he needed to see the vet. But even then, I wasn't expecting heart disease. I thought the hypercalcemia was causing issues again.