According to the American Heartworm Society, the gold standard of treatment for heartworm is a several month process in order to reduce the risk for serious complications and side effects:
Day 1–30. Pretreatment with antibiotics
Day 31–59. No treatment
Day 60. First dose of Melarsomine
Day 61–89. No treatment
Day 90. Second injection of Melarsomine
Day 91. Third and final injection of Melarsomine