mosquito and heart worm for Sorbet

Sorbet is 4 year old mixed dog and he is very food-lover. We live in Saraphi, near the rice field so mosquito is so many in the rainy season. Last year he get heart worm test, it was negative but vet say we must give medicine every month anyway. We give the chewable one with breakfast. Sorbet think it is snack. Very good. I forget 1 time in October and I call vet in panic, they say give it now and check blood later. Dont make the same mistake. Also mosquito spray for body, but not on face and not near his eyes. Thai people also use the coil at home, which is bad for dog breathing, so we use fan instead.