none of these dogs had heartworm in the heart and lung arteries at necropsy 6-10.8 month post infection, whereas, the three control dogs had 27, 26, and 21 worm, respectively. in a recent study involving dogs with naturally acquired infections, a combination of doxycycline administered at 10 mg/kg once daily for 30 days and prophylactic doses of ivermectin administered every 15 days for 6 months resulted in 72.7 percent (8 of 11) of the infected dogs becoming atigen negative and 85.7 percent (6 of 7) becoming negative by echocardiographic visualization of worms at Day 300