[quote user="ColleenC"]Actually, hearworm meds don't stay in the system. [/quote] ColleenC is correct. Interceptor and Heartgard are out of the dog's system in 24-48 hours. The "preventatives" prevent adult heartworms by killing immature heartworms. Heartworm "treatments"...

Maybe this will help: Heartworm " preventatives " kill baby heartworms and are given monthly. Heartworm treatments kill adult heartworms and are very hard on the dog. Janie can be tested right now for adult heartworms.