I purchased Nexgard Spectra for my Shadow. He is now 3 and healthy as ever. I have been giving him heartworm preventive since my veterinarian told me to. So, I started purchasing heartwormers from BudgetPetCare.com. I am so relieved with the efficiency of the product. It has never failed me or my son Shadow. I guess he doesn't even know it's a medicine I am giving him.