I lost my precious baby Frasier

Question:
 On Tuesday July 20, 2004, I lost my little Jack Russell Terrier Frasier. For about 2 months he had been having lose stools. We took him to the vet and they told me he was having a reaction to new allergy medication we had put him on it was called Atopica. We reduced his intake of it and eventually took him off of it. His diarreah persisted and they said he had an infrection so they put him on antibiotics. These did not help and he would occasionally vomit. We then took him in last Thursday and they told us that he still had an bacterial infection. They took an Xray and found no blockages of any sort. We also told them that when he got sick he would get week and collapse. Well he did not get any better so we took him back in on Monday and they ran a blood test. We also told them that he was acting strangely and showed aggression towards us which was unlike him. On Tuesday he lost all appetite and we took him back in to hospitalize him and to get more tests run. That night they told us that they had him on an IV to give him fluids and he was walking around in his cage. The vet tech said she had just checked on him and he was fine when she came back around moments later he had passed on, that was four hours after we brought him in around 9:20 P.M. We went to the vets office on Wednesday to say goodbye to our baby and to arrange for him to be cremated. The doctor came to see us and said to his best knowledge Frasier had passed on because of a heart attack. I heard that this is very uncommon in dogs is that true? What else could have caused this? I can with absolute certainty guarantee he did not get ahold of any poison. I must also point out that in the beginning of march we had taken him to an eye specialist because he went suddenly blind. The eye specialist diagnosed him with Sudden Aquired Retinal Degeneration. And said that though this was not curable he would be able to adjust and suffer no adverse health affects from it. In those two months he had been to the vets over seven times. I just can help but think that they missed something or maybe I missed something. He had a hard life before I rescued him, he was abused for about a year of his life. He was only 10 when he passed away. I cannot seem to think that maybe we should have done something different he would still be here. I have three other little dogs and I just cant seem to move on. I have grieved and grieved and have no drive to do anything. I know he is in a better place and I hope he knows that I love him and I hope that he loves me. Sorry for the long post I am just to overcome by this tragedy. I will always love him.
Answer:
 i have lost many pets to tragic events . some shot in the head, old age, my horse was even slagtured but none as tragic as my lucky boy.. he is a big fat black and white cats. he was crossing the road one rain day when a man saw my cat in the middle crossing . my cosin and father ran in to the road telling him to slow down but he just spead up...then it was all over. he had ran over his head, and my lucky was killed instinly..2 days laters my cats smopkey was hit ...then befor chrost mas my cats pearl died.. i have gotten 3 cats sence lucky but none of them will ever take his place..i am olny 13 years old and have dealed with so much heart break . but i know with all the pain i feel..all of my animals feel none because they are all up in heaven...waiting for me..
Answer:
 From your description, I would wonder about the possibility of Addison's disease aka/ hypoadrenocorticism. Also, possibly a brain tumor, but that would not necessarily explain the diarrhea. Unfortunately there is no way to know for sure. I'm sorry for your loss.