New Heartworm Guidelines are available from the American Heartworm Society (AHS). These recommendations are based on the latest information presented at the 2007 Triennial Symposium, new research and additional clinical experience. Guidelines for diagnosis, treatment and prevention of heartworm infection in cats are contained in a separate document.
Canine guidelines: http://www.heartwormsociety.org/veterinary-resources/canine-guidelines.html
Heartworm infection in dogs has been diagnosed around the globe, including all 50 of the United States of America (USA). In the USA, its territories and protectorates, heartworm is considered at least regionally endemic in each of the contiguous 48 states, Hawaii, Puerto Rico, U.S. Virgin Islands and Guam. Heartworm transmission has not been documented in Alaska; however there are regions in central Alaska that have mosquito vectors and climate conditions to support the transmission of heartworms for brief periods.