Heartworm is treatable, its really expensive and takes time but treatable.
It boils down to a personal choice, here we test annually and should they ever have it clearly we would treat it. Financially though we are blessed to be able to make that call if finances were more of an issue I would use preventatives.
We are in a heart worm area but take very drastic measures to keep the dogs out of mosquitos as best as we can. It is far more of a hassle but to us, worth it
Courage is being scared to death and saddling up anyways. ~John Wayne