This is a 12 pack of RSPCA Monthly Heartworm Tablets for large dogs 45-88 lbs (21-40 kg). This 12 month supply of heartworm tablets for large dogs comes in 2 x orange 6 packs. Each tablet will treat your dog for 1 month. These tablets prevent heartworm disease in dogs 45-88 lbs (21-40 kg). It prevents heartworm disease in dogs by elimination the tissue stage of heartworm larvae that infected the dog in the 30 days before treatment. It can be used on puppies from 6 weeks of age.