The Heartgard brand is among the most trusted heartworm prevention medications, and for good reason. In terms of keeping your dog safe from heartworms, hookworms and roundworms, Heartgard Plus Chewables (ivermectin + pyrantel) for dogs has your pooch covered. When given monthly as directed, it is effective in helping to prevent heartworm disease. Heartgard Plus kills immature heartworms that have been introduced to the dogs within the last 30 days. It is also an effective treatment against some other parasites, including ear mites. Approved for puppies as young as 6 weeks, pregnant or breeding female dogs and stud dogs.