Tri-Heart Plus Chewables for Dogs are used to prevent canine heartworm disease and for treatment and control of roundworms and hookworms. Tri-Heart Plus contains ivermectin and pyrantel. When given monthly as directed, it is effective in helping to prevent heartworm disease. Tri-Heart Plus kills immature heartworms that have been introduced to the dogs within the last 30 days. Tri-Heart Plus is also effective against canine roundworms and hookworms. Approved for puppies as young as 6 weeks, pregnant or breeding female dogs, and stud dogs. Ivermectin and pyrantel.