My little dog Ziggy had his first annual check up with my favorite vet. He had all his intial shots and neutering by his first owner and then the rescuer got him another exam, had him on heartworm meds and Frontline when I got him. I continued on with them till winter and stopped. I didn't start the Frontline yet because I read about complaints last week and also I wasn't sure what strengh to give him since he weighs 22.7, and I think the cut off is 23 pounds. I didn't want to over dose him. Anyway vet prescribed Sentinel to use year round and gave me a 12 pack. Well didn't give me..it was $123.00. He says it's great for heartworm, other parasites ,and fleas, but needs to be given every month. He says I may not need Frontline too. I have never used it before . Does anyone here use it and are you satisfied? I gave him his first pill tonight. Vet also said he has a tiny heart murmur which is hardly detectable and means nothing.