The treatment is toxic and usually fatal to cats. Therefore the only thing we can do is put the cats on heartworm preventive and treat for congestive hear failure if it has developed. I have had some people say my dog or cat rarely or never goes outside. But remember that the disease is spread from one dog or cat to the other through the bite of a mosquito and only through the bite of a mosquito. The larvae of the worm must mature to a certain stage in the mosquito to be infective.
Mosquitoes have easy access to anyone s home.
So it is like Russian roulette not to have them protected by heartworm preventive. Once the pet is bitten by the infective mosquito the larvae take about 6 months to reach the heart and mature into adult heartworms. The preventive works by killing these larvae in the tissues each month before they can ever reach the heart. So as you can see heartworm protection is the way to go. This disease kills just as dead as the viruses we vaccinate against.