Yeah, to me, heartworms is just... not something I wanna mess with nor risk.
With that said, my dads dogs have never had heartworm prevention, at least in our care and I think it's really ignorance over negligence or not having money or anything. I've mentioned it a few times, how it's important, how you need a prescription to get it, and my step-mom always talks about "oh yeah, I keep meaning to get that". She treats it as we would flea/tick meds. Eh, I just don't push it. I try to help out whenever possible with their dogs but at the end of the day, they're not my responsibility and they've never caught heartworms yet. And their outdoors often but only in our backyard. So who knows.
To me, it's one of those important things I don't miss.
Brit & Jackson