If the heartworms did any permanant heart damage, this can affect circulation in the little guy and that in turn can affect the hair and skin, but changing his poor diet can make a mountain of a change for him. His teeth of course can be cleaned, if theres any broken or rotten one, they can either be filed down to where they aren't having any sharp edges or they may need to be pulled
. People just have no idea what effect neglecting our pets can have on them. It really upsets me. At least he has you now. I would definately have him checked out by the Vet. and make sure his heart if OK. If the heartworms were treated early, he more than likely has no damage and will be fine with some TLC and good food. Good luck with him. I hope you come back and tell us how he's doing.
Steph