Talk to your Vet.

Our Dr. Mike always suggested giving heartworm preventative for all 12 months -
he feels there is always the possibility of a mosquito "living through the winter".

A few years ago I skipped their January HeartgardPlus ... and a week later
found a couple Live Mosquitos flying around in the garage on a warm day.



We've been on an all 12 months schedule ever since.