1-25 heartworm cases in my area, is this enough for preventatives?

I have a dog and an indoor cat. I have always given heartworm meds to my dog but I have not put my cat on anything since I've had her. According to the incidence map for 2013, there were between 1 and 25 cases. We do have mosquitoes in the house from time to time in the summer, as I guess a lot of people do. Everytime I find one I cringe because my cat is untreated. At the same time, I hate to put chemicals like that in her system.
With an incidence like this, what would you do?

Good question ..

Our dogs are tested every year and on Heartworm prevention year round but  I have never thought of it for your Indoor cats ..

I did not even know they made Heartworm preventatives for cats .

correction : that should read " for our indoor cats "

I've just been reading about heartworm in cats today. Apparently there is no treatment for cats if they get heartworm, you just try to manage the symptoms and hope the cat survives.  My state has a very high incidence of heartworm in dogs, and we've always kept the dogs on prevention year round. I'm wondering now if I should be giving the cats a preventative too. I'm interested to know whether anyone on here uses it.

I take my cat out on a leash and use Revolution.  This is the best heartworm preventative for cats.