Guiness and thyroid

I dont know if I ever talked about this so I will now.   Guiness was having trouble going on walks that started over a year ago.(maybe even 2 years)   Most of the time he couldnt finish the hike and would just lie down.  The first couple of times this happened , I checked his heart rate and it was 70.  Kinda low for a dog that is hiking up and down hills.  We carried him back to the car. Sometimes I would leave him home because I just couldnt carry him.  He had stopped playing with toys.  When we went to the beach , he could only tolerate one walk a day.  Even though he had the whole day to rest for the second walk, he just refused to go.  If he ran around the yard at home, he would come in the house panting so hard it was scary. He would just lie down breathing very heavy.  I took him to the vet and asked multiple times if it could be his thyroid.  I always got the answer "no". ( He doesnt look low thyroid. Not fat, not loosing his hair)  They did an EKG. Normal except for a low heart rate. They sent us to a internist to have his heart check. He had an ECHO it was normal, except for the low heart rate.  I asked again about thyroid. "no".  His level at the time was 1.4   (there low was .8) .   They started him on Theophyilline to increase his heart rate. It did increase it but didnt help any of his symptoms.  I think I gave for 6 months and then gave up.  The next time he went for his yearly check up his thyroid was 1.   His BUN was up 1  point. They wanted me to bring him in for some follow up test for the BUN.  Ok, one point on a BUN is nothing especially since is Cr was normal.    I lost it. I told them I cant believe they want me to come in for this but will do nothing about his thyroid that just keeps decreasing and he has all these symptoms. I said, "Are you waiting for my dog to die?".    Well, I guess that did it. So they started him on thyroid medication. LOL  So even though his level has only increased to 1.8, he is a new dog.  Plays with toys again. Can run around the yard and bark without  looking like he is going to die.  2 walks a day at the beach, no problem.  And has not stopped on any walks even when hiking.  So when the vet tells you it isnt the thyroid because the number hasnt dropped low enough, keep fighting.