What's Wrong With This Dog?

Just over a month ago, Rowdy got off of his food and started breathing excessively heavy or fast. I became real concerned, so I took him to the vet to find out what was wrong. They did a physical exam and blood work testing and found nothing wrong. Then they tested him for heart-worms and found he was infested with them. Still don't know if this is what was causing him not to eat or his fast breathing, but at least we found something.

The first part of his treatment was a month on 100 mg Doxycycline twice a day. This was to weaken the worms, so the treatment would be more effective in killing them out. Then he would have his first treatment which would be a single dose for a month and then two doses for his second treatment a month later. While on the Doxy., after a week his breathing returned to somewhat normal and his appetite returned. I wondered later if his initial problem was that maybe he had been poisoned. That fits a better description or cause of the initial problems he was having.