For: Dogs (6 weeks of age or older and no weight requirement) Cats (8 weeks of age or older and no weight requirement) How it works: Revolution works by penetrating the skin and entering your pet's bloodstream. Concentrations of selamectin, the active ingredient, in the tissue and bloodstream prevent heartworm disease. Selamectin also redistributes into the skin from the bloodstream and kills adult fleas, American dog ticks, and ear mites, and prevents flea eggs from hatching. It is also an anthelmintic, which means it fights to expel parasitic worms. Parasites ingest the drug when they feed on the animal's blood. Revolution is safe for pregnant and lactating pets. Cautions: Side effects are uncommon, with less than 1% of dogs showing signs of digestive upsets. It is not advisable to use Revolution in pets that are ill or underweight. Collies and herding dog breeds may have a reaction to the ingredient selamectin if given over the recommended dosage amount. If your dog is a collie or other herding dog breed and your veterinarian has prescribed Revolution, we urge you to monitor your pet for 8 hours and call your vet if your dog displays any signs of weakness, staggering, dilated pupils, trembling, drooling, or pressing his or her head against a wall. Directions: Apply Revolution once a month on the same day of each month year round. Use the entire contents of the tube. Do not split the contents since the dose and therefore the effectiveness of the product can be reduced. Part your pets hair at the base of the neck between the shoulder blades until you can see the skin, and place the tip of the tube on the skin. Apply the contents of the tube to a single spot on the skin at the base of the neck between the shoulder blades. Tip: Revolution is quick drying. The pet can be bathed 2 or more hours after applying.