Revolution is the most complete flea and heartworm protection for cats. It provides dual protection from fleas and heartworm in a convenient monthly spot-on. Why do I need parasite protection for my pet? Parasites aren't just a nuisance - they are a real threat to you and your pet. Heartworm disease can be caused by a single mosquito bite and can kill both cats and dogs. And fleas make your pet uncomfortable and cause flea allergy dermatitis the most common skin allergy in dogs and cats. Fleas also transmit tapeworm to dogs and cats not to mention the trouble a flea infestation can cause you.