P.P.
We just put our beloved 13 and a half year old to sleep this past monday. But we did everything we could over the past year to help him have a happy and comfortable life and spent quite a bit of time, energy and money. Aside from a lot of panting and just a bit of stiffness, that dog was happy as a clam and slept like a rock.
He was on Deramaxx which he tolerated very well for arthritis.. he would jump off the back step to go to the bathroom until the last week of his life. He had a tumor in his lungs but even the vet agreed it would be unfair to put him through chemo at his old age. Fortunately the tumor grew VERY slowly and the vet said the panting could be from that in his lungs.. or the fact that he was anemic.. or some dogs have a larygeneal (sp) throat sort of issue that makes them pant.. or in your case.. maybe he does have a heart condition. If you are a pet owner like we were.. I would do as many tests as you can afford to get to the bottom of this. We did what we felt was absolutely necessary but if he hasn't had a complete blood work up.. urinalysis and thyroid test.. you really should invest in these if you don't want to put the animal to sleep. What quality of life does he have if he is so upset and most likely in pain all the time? if he isn't sleeping.. he is in pain.
I know panting can also indicate pain so my gut says, he is in some sort of pain. A good blood work up is a great place to start. And perhaps you are going to have to invest in a ultrasound of his heart or something like that. It could just be a matter of getting some proper meds for him and that dog could live another year, maybe even more.
please let us know how it goes at the vet office!