When it comes to our feline friends vs heartworms... the heartworms will always win.
Prevention is the key
Cat's hearts are so very small, that as few as 3 heartworms can produce serious illness and death.
Worst of all, there is NO CURE, NO TREATMENT, NO RECOURSE for your cat if he becomes infected. The veterinary industry has developed heartworm preventative medications that can keep your cat from infestation. Cats do have an advantage over dogs in that they are more resistent, but as the prevelence of heartworm disease increases, the likelihood of developing the disease increases.
Ask your veterinarian about heartworm prevention for your cat or kitten.