If you're talking about more than one pet (we have six) then you're not saving only $10 or $20. You're talking several hundred dollars per year. You do not need your vet's permission or prescription to order heartworm or flea medication online from Canada or Australia. I also woulnd't support a vet that would pass judgement upon me for shopping around. I posted links to two very reputable companies that have been in business for many years. Ivermectin and topical flea medications (like Advantage and Frontline) are NOT prescription medications in most places!! You can legally buy Advantage and Frontline over the counter from ANY American online pet store and from several places locally. You do not need to pay your vet's markup price for the exact same product. Heartworm protection is not available in the US (for dogs anyway -- cattle farmers always have access to it) without a prescription, but it is available in just about every other country without one. I'm not suggesting that anyone abandon a vet they love, only that there are other (more economical) options for those who don't mind doing their homework.