Since there are a lot of mosquitoes where I live, we have the dog on heart worm medication to be safe. (web-dvm.net)
Your vet may offer special seasonal promotions for heart worm medication or vaccinations. (americanhumane.org)
Additionally, quality flea and heart worm medications like revolution kills almost all worms along with the fleas and ticks, but they are often more expensive sometimes quite a bit so. (caninejournal.com)