Can I do anything in my cat’s environment to reduce the risk of heartworm? - Animal Hospital of Statesville

Preventing standing water is essential. You can use area mosquito sprays and things like that, and they are safe if you follow directions. Anything you can do to keep the mosquito population down in the area helps. Usually, that is combated by avoiding standing water in those areas, dumping standing water from your flower pots, and other things like that.

Can I do anything in my cat’s environment to reduce the risk of heartworm? - The Drake Center

Keeping your cat indoors will greatly reduce the risk because you're going to have fewer mosquitoes in your indoor environment. That doesn't mean a mosquito can't come into your house now and then. I kill them from time to time in my own house. But keeping them indoors does lower the risk of heart disease and cats.