They should be treated as indoor pets as they are very sensitive to cold temperatures. (dogingtonpost.com)
However, even indoor pets become infected by heartworms as infected mosquitoes can, and do, get into houses. (catclinicofjc.com)
These larvae can easily hitch a ride indoors on the shoes or clothing of family members, making fleas just as much a concern for indoor pets as for those that venture outside. (articles.extension.org)