Heartworm is something we all need to help prevent for our pets.  The best action against Heartworm is prevention!  
Here are some facts:

How does my dog get heartworm?- Only by the bite of an infected mosquito. There’s no other way dogs get heartworms. And there’s no way to tell if a mosquito is infected. That’s why prevention is so important.

Heartworm disease has been reported in all 50 states. And the bite of just one mosquito infected with the heartworm larvae will give your dog heartworm disease.

It takes about seven months, once a dog is bitten by an infected mosquito, for the larvae to mature into adult heartworms. They then lodge in the heart, lungs, and surrounding blood vessels and begin reproducing. Adult worms can grow up to 12 inches in length, can live 5-7 years, and a dog can have as many as 250 worms in its system.

PREVENTION:
For less than the cost of going to Starbucks for a weekly coffee, you can prevent heartworm disease in your dog. There are monthly pills, monthly topicals that you put on the skin, and there’s also a six-month injectable product. The damage that’s done to the dog and the cost of the treatment is way more than the cost to prevent heartworm disease. A year’s supply of heartworm preventative will cost about $35 to $80, depending on a dog’s weight.

So contact your local veterinarian for details (the Veterinary Specialty center does not sell heartworm preventative)