Generic tablets are NOT chewable. Heartgard Plus is the no. 1 choice of veterinarians for heartworm disease prevention! Heartgard Plus is 100% effective against heartworms and it controls roundworms and hookworms. Heartgard Plus is approved for use in puppies as young as 6 weeks of age. It is safe for pregnant or nursing females, stud dogs, collies, and dogs with collie genetics.