I use the Revolution on all my girls. They have never had a flea or tick and I love that it is dosed closer to their actual weight. Princess gets the <5 lbs. and my others get the 5-10 lbs. It has the heartworm and the flea in one topical dosage. I have used it for about 8 years and never had a problem with it. In Texas, we must treat year round since the fleas and heartworms are always present.
Be sure and get your babies checked for heartworms before giving them anything for it. They will need to be HW negative before starting any treatment.
We get it from our vet.