Heartworm preventatives and pups

I just had a thought when I picked my son up from school. There's a 9 week old white GSD pup who gets to come along (I bring Lacey with me to pick him up if I don't have the little ones with me - it's good socialization for her and she gets mauled by kids, which she seems to enjoy) but at what age do puppies start HW preventatives?
What about pregnant bitches, are they given HW preventatives on a regular schedule, what about bitches that have already whelped?

Puppies can start on HW preventative at around 3 months old depending on location and season. A heartworm test is usually suggested to be performed at 6 months old, due to the life cycle of heartworms. Annual tests are recommended after that initial test provided the dog is kept current on medication. These are general suggestions, there are different thoughts on this of course that will vary based on location, climate, type of vet practice, and personal beliefs.
Cats can even get heartworm, although it is not as common as dogs testing positive for heartworm, and unlike dogs, the prognosis and treatments are not as optimistic. I saw a kitty this year that had heartwormed dx by x-rays. Poor kitty did not make it.

Boy , it's been a while for me , but all my dogs were up to par health wise and I bred to only the same , all pups whelped were checked from day one . I never had a pup with any parasites /

I start all my pups on hw prevention at 8 weeks. And any pregnant female stays on hw prevention...there's absolutely no reason to stop it for those 2 months (or longer if pups are born and bitch is nursing).