Heartworms are transmitted through the bite of an infected mosquito.  When a mosquito bites an infected dog, it picks up microfilaria (baby heartworms) along with the blood.  The microfilaria develop in the mosquito and when the mosquito bites an uninfected dog the developing heartworms infect the new pet.  Once introduced by the mosquito bite, they migrate to the heart and develop into adults.  Heartworm infection is a very serious condition that can result in problems such as heart failure, liver failure, kidney failure, and death.  Heartworms are easily prevented but your pet must be tested prior to beginning heartworm preventative.  We currently have an oral heartworm preventative that must be given monthly or an injectible preventative (we give the shot, you don't) that is good for 6 months.