Heartgard Plus Chewables For Medium Dogs 12 To 22 Kg Green is a vet-recommended heartworm disease prevention treatment that also controls and treats intestinal worm infections. HeartGard Plus is highly effective against immature stages of heartworm that are transmitted through a mosquito. It also treats and controls four species of hookworms and two species of roundworms. This monthly treatment has antiparasitic and anthelmintic properties that work against mixed parasitic infections, protecting your dog from potential health problems.