Heartgard® Chewables (ivermectin) for small dogs (up to 25 lbs) is a once a month beef-flavored chewable tablet that can protect your dog from the threat of potentially deadly heartworm disease. Heartgard Chewables are approved for use in puppies as young as 6 weeks, small dogs regardless of weight, pregnant or breeding dogs, and Collies. Dogs 6-months of age and older should be tested for heartworm disease prior to being put on a preventive program and tested annually thereafter. (Heartgard Plus is available only through prescription from a licensed veterinarian.) Heartgard Chewables are also available for medium (26–50 lbs) and large (51–100 lb) dogs. For dogs over 100 lbs, mix and match to reach the appropriate weight range.