[gemy]

A HW positive dog is not infective to other dogs or humans. What is positive about this response from the rescue is their honesty and clarity of his issue(s).

Speak to your vet, and speak to the vet who is treating this rescue for HW, to get an idea about the severity of his infection. For example on XRAY were heartworms visible on exterior heart wall?

Then the rest of it, centers around how your current dog will interact with the new rescue. What is the personality like of this rescue? How active/quiet, etc is this dog?