I am debating whether I should give Aspen his Heartgard this month, or next. I really would not like to give it to him if I could, but we can't escape mosquitoes here in the spring and summer. I have already eliminated k9 Advantix for the winters, but I have to use it in spring and summer because the fleas here are terrible! I don't have to worry about ticks though. There are no mosquitoes here right now, but is there a chance that a few mosquitoes might come in and infect him?