I give Mojo heartgard from Merial. I checked on their website and has good information about the disease and the need of a prevention treatmennt. Heartworm disease has been found in all 50 states in the U.S.
You can read about it at :
http://us.merial.com/pet_owners/dogs/heartworm.asp
They also have a map (at
www.heartgard.us.merial.com) for the cases of heartworm diseases:
http://heartgard.us.merial.com/pix/i...ce/map_usa.gif
(the top ten states in ocurrences are marked in red)