As a subject matter expert in veterinary medicine, I can explain the mechanism of heartworm prevention in dogs. Heartworm pills, also known as heartworm preventives, are designed to protect dogs from developing heartworm disease. The life cycle of a heartworm begins when a mosquito bites a dog and transmits the heartworm larvae. Once inside the dog's body, these larvae mature over a period of months into adult worms, which can cause severe damage to the dog's heart and lungs. Heartworm medications available today work by targeting the larval stage of the heartworms. They are effective in eliminating the larvae that have entered the dog's body during the previous month. This is crucial because the sooner the larvae are killed, the less likely they are to develop into adult worms that can cause serious health problems. However, it's important to note that heartworm preventives are not effective against adult heartworms that are already established in the dog's body. If a dog already has adult heartworms, a different treatment protocol is required to address the issue. In summary, heartworm pills are a form of preventative medicine that can stop the development of heartworm disease by killing the larvae before they have a chance to mature. read more >>

If an infected mosquito happens to bite your dog, he/she may still be infected with the larvae. Heartworm medications available today work to kill off the larval heartworms that made it into the dog's body during the past month. ... However, heartworm preventives will not kill adult heartworms that are already present.read more >>