I heard it damages the liver.
Answers (2)
If your vet recommends canine heartworming pills for your dog (which they should) then it shouldn't be harmful. Not vet is going to trick you into risking your dogs health for more money. (I also stress CANINE pills, never give feline medication or any other animal or human medication to your dog unless told by vet in a consult in which the vet has assessed your pet thoroughly)
You do NOT want your dog to get heartworms. Some myth of live damage? Pheh! Try having hundreds of worms growing inside or your heart!
Always provide proper protection from heartworms, fleas, ticks, worms, and other intestinal parasites.
However it may interest you to hear that yearly vaccinations for dogs are being researched currently and the findings are suggesting that giving the vaccinations once a year may actually be harmful to some dogs. There may be a possible cut back to once every three years for some breeds. DO NOT stop vaccinating your pets though, discuss with your vet and go with what they think is the best course of action. This research is only new...
No, if you are taking according to the prescription of Vet. I have been using Trifexis which is easily available on petcarerx.com at best price. Mosquitoes are the major source that can spread heartworms in your pets. When they suck bloods of infected animals, larvae of heartworms transmitted to other animals by their bites. So its good to take immediate action before the problem gets out of control.