[Roxybear]

Hi folks. I'm new but excited to be registered! I have a question. My 8.5 year old yorkie, Roxy has had 3 walks per day most of her life. Of my two dogs she was always in tiptop shape and the leader of the pack, often looking back to see what was taking us so long. In late spring, she began slowing down and stopping during a walk. I thought it was the high humidity at the time. Intermittently she appears to have a spurt of energy and then slows right down again. As of today, she walks quite slowly and often lags behind, waiting to be picked up! This is so out of character.
I took her to the vet last week, who checked her heart and all of her joints in case she had arthritis. No ultrasound for the heart. Blood and urine was taken and all was normal.
I'm worried and think it might be her heart. She also had loose stool this weekend and has thrown up her brown rice meal two out of three times. I'm stumped. Is the brown rice hurting her? I'd hate to think I was making thing worse!Help??