Parasites like fleas, heartworms, ear mites, lice, tapeworms, roundworms, hookworms, etc. can not only be a real nuisance, it can also cause your pet serious harm.
Revolution is a very helpful medication that can help treat and prevent many of these issues.
Read more about it and how these situations occur: Revolution | Flea & Parasite Treatment for Cats | RevolutionCats.com
Revolution can be prescribed by your vet. Ask them for more details.