Often thought of as only a disease in dogs, heartworms are just as dangerous for cats, if not more so. Dogs are the preferred host, but studies show cats are as susceptible to heartworms as to feline leukemia and feline AIDS, and there is no real treatment for feline heartworms. Although there are treatments for canine heartworms, those treatments are expensive ($500 and up depending on the weight of the dog), and if the disease is advanced enough the result can still be death. I’ve witnessed this first hand with a foster dog who was infected with heartworms, underwent treatment, but still died a few weeks later. Treatment of the disease does not mean there was no damage to the heart, and that damage can be extensive enough to kill.
With both dogs and cats, the answer to heartworm disease is prevention. Unlike treatment for fleas and ticks, heartworm medication requires a prescription. An annual blood test is required, then a pill once a month protects pets from heartworm disease. Most animals even like the taste of the medication.