Heartworm Disease Can Be Prevented.

Monthly heartworm prevention is very effective in preventing heartworm disease. Make sure you keep your dog on heartworm prevention ALL YEAR LONG. Annual heartworm testing is done to make sure your pet does not have heartworm disease. Ask your veterinarian about a test called Accuplex or 4DX - a blood test that tests for heartworm disease as well as tick borne disease (Lyme, Erlichia and Anaplasmosis). Tick borne disease are on the rise throughout the US. Flea and Tick prevention is definitely recommended for all dogs and cats. 
A picture can speak a thousand words about heartworm, and the brand-new incidence map from the American Heartworm Society is no exception.
http://www.heartwormsociety.org/download/AHS-2013-Incidence-Map.pdf