My 14 week old pup has been on Revolution for the past two months. The vet also gave him some Heartguard plus for heart worm prevention. I was going to order some more Revolution when I read that it also protects against heartworms. Do I need the Heartguard plus since Revolution protects against heartworms? If so, then I am going to switch to Interceptor as soon as his 3 month Heartguard supply runs out.