Heartworm Treatment Update:

Our Visit yesterday with the vet was informative. Rex has the shot that slowly kills the heartworm. 
As the worms die small pieces at the end of the worm break off and go into his body where the body deals with them.  It is imperative that he be kept calm all the time because if his heart rate increases there is a definite risk that larger pieces of the worm will break off and they can lodge in his lungs and other parts of his body in the form of a clot that can kill him. 

So we have to keep him calm for the next 90 days to avoid that from happening. He can go out two times a day to go potty and Rex can have no activity that will increase his heart rate like guests and such. We have a crate for him but he doesn't have to stay in it as long as he can stay calm. Our vet does not treat heartworm in the summer months because the heat can cause an increase in the heart rate.