When should I start heartworm prevention for my cat? - The Drake Center
This is a great question because it depends on where you live in the country. Heartworm isn't a common disease in California. It's much more common in the Midwest, along the Mississippi River, the Gulf Coast, and the East Coast. So it depends on where you live as well as the lifestyle of the cat. If the cat lives outdoors, they should be on prevention year-round, especially if you live in those areas. I would start it when they are kittens as young as eight weeks.