How effective is heartworm prevention for cats? - Animal Hospital of Statesville

Heartworm preventions are 95% effective or more if administered properly and given regularly.

How effective is heartworm prevention for cats? - The Drake Center

It's completely preventable if you are diligent about giving it at the recommended time. If you give an oral preventative once a month and you never falter from that, your cat will not get heartworm disease. It's a hundred percent preventable.