I have been using Advantage on my sheltie for ticks and fleas for my sheltie for many years and last year it stopped working for ticks. My vet said to buy a tick collar for those months when ticks are a problem and that seems to work but I am wondering about using Revolution for Summer. I bought some for the cat but have not applied it as yet. My question about Revolution is that I don't know what kind of medicine it uses to prevent heartworms. I have been using Inteceptor instead of Heartguard because of the problems that some collies and shelties have with the ingredient in Heartguard and I would not want to use Revolution if it contains the Heartguard ingredient. Does anyone use Revolution for their sheltie? I really think it would be easier to just apply one medication instead of giving two plus the tick collar but don't want to endanger Summer's health. TIA.