The therapeutic protocol for treatment of canine heartworm disease recommended by the American Heartworm Society consists of 3 intramuscular injections of melarsomine, with steroid and antithrombotic agents as needed. This regimen has long been the basis for heartworm adulticidal therapies and is safe and effective when used as directed; however, melarsomine periodically has limited availability and is unavailable in many countries. Thus, many slow-kill protocols have been circulated as possible alternatives when melarsomine is unattainable. Critics of these techniques have argued that dogs with high worm burdens would be at greater risk for complications (eg, pulmonary and systemic inflammation, pulmonary thromboembolic events, myocardial ischemia) related to their worm burden. In addition, it is assumed that dogs with a higher worm burden would be more resistant to effective long-term elimination of disease with a slow-kill protocol.