Heartworm is a nasty disease transmitted by mosquitos. Since mosquitos tend to be fierce in the area, we recommend keeping your pet on a heartworm preventative year round. The products used as a preventative have a high effacacy rate but unfortunately cannot be 100% effective. Therefore we recommend yearly heartworm testing. Declining the annual heartworm test can put your pet at risk for either having adult heartworms or developing a serious reaction from the administration of the preventative medicine.
Heartworm Society - Everything you ever wanted to know about heartworm disease can be found here!
Heartguard Plus - HEARTGUARD Plus is the easiest heartworm preventive for you to give your dog each month. It's the only one that comes in the real-beef Chewables that dogs prefer to take and owners prefer to give
Novartis Animal Health - This site is sponsored by Novartis, the makers of Sentinel, Interceptor and Program, and has useful information on heartworm prevention and flea control for pet owners.