re: Dog Heartworm Lifecycle has changed?

Long story short there has been extensive research on the Heartgard/Ivermectin breakthroughs. The breakthroughs are much too common to consider it as an effective med for heartworm prevention. Moxidectin is now the most current and effective active ingredient in effective heartworm preventatives. Moxidectin is the active ingredient in Simparica, Proheart, along with some others. Moxidectin is not 100% effective though, I am aware firsthand of 3 confirmed breakthroughs of Proheart in the last 2 years. Proheart will cover the heartworm treatment as long as a negative test was on file before the proheart was administered.

There is also some off label use for Simparica Trio being used as a slow kill effective method currently by some vets.