All puppies are born with worms (roundworms) which are passed to the pups from the mother while pregnant. You will probably NEVER see these unless the pup has a very heavy load of them. They can also vomit them up if they have a huge load. That is why puppies have those cute pot bellies we like so much, unfortuanltly that is a belly full of worms. Now tapeworms are the worm you will see, they look like a piece of rice. and they are caused by fleas. The flea carries them and will be on the dog or cat and when the animal cleans itself it will ingest the flea and that how they get it. another way it by hunting (cats do this more) eating rodents with fleas on them and thats another way of getting tapeworms. At the clinic I work at we will send a dose of Drontal and then follow it up with a pyrantel (strongid) dose in 2 weeks. By all means do take in a fecal sample and have it checked. That is the lovely part of my work that I do all day, checking fecals...oh its so much fun...NOT.. And the heartworms, they are tramsmitted by mosquitos. It takes 6 months for the heartworm to be identified on a test after the mosquito bites the dog and injects the heartworm into the body. It takes a while to try to explain the process and i dont think i have enough room on here. Here in the Northwest we really dont have all that big of a problem with heartworm, but there are a few pocket areas that are bad. If your dog travels with you to other states or out of your area I would have them on preventive all year round. And Heartgard (brand of preventive) also controls 3 kinds of interstinal parasites. Whipworms, Roundworms and Hookworms. Heartgard or Interceptor do not control tapeworms.