Was there a gap in prevention that left this dog susceptible?

The “Window of Infection” is the time frame when a dog was likely infected with Dirofilaria immitis to result in a positive test for adult heartworm.

This time frame is based on the pet’s heartworm testing history and the life-cycle of Dirofilaria immitis. It extends from 6-9 months prior to the dog’s last negative test up to 6 months before the current positive test.