It is an alteternative that the AHS ( American heartworm Society) recommend only for dog in which an adulticide is too risky. It can take years for Ivermectin ( the only preventative nown to kill adults) to be effective It realy will only kill adults 7 month and younger but sterizes females so they can not reproduce and the older worms dies natural. It is posible for then worms if not treated with an adulticide to continue to do damage to the heart and lungs so the general recommendation is to use an adulticide to kill the worm in a two stage approach it minmize throbosies cause body the breakup and decay of dead heatworms when killed.
see 2005 Guidelines For the Diagnosis, Prevention and Management of Heartworm (Dirofilaria immitis) Infection in Dogs