Quote Originally Posted by areias
Heartworms are treatable, although it shortens the dogs lifespan by treating. They inject the dog with a form of arsenic, and although treatment can be fatal, it's not usually. A lot of shelters/pounds won't treat for heartworms, it is very costly. For the average person it's $500-$1000 to treat, if you get the drug (immiticide) like as a vet, it's probably about $300. Not worth it to a lot of shelters.
Thanks for the info -- I didn't know that!

I've always had all our pets on the preventatives (even the ferrets!) to be on the safe side.