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

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.

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.

Keep water moving in your cat's environment. Avoid stagnant water. If there are any bowls left outside, rinse them and keep them as clean as possible. Also, try to control the mosquito population as they play a role in transmitting heartworm disease.