If you are importing (or have imported!) a dog from Japan, heartworm is something you need to be aware of. It is widespread in Japan, and unfortunately many (most?) NIPPO members do not give their dogs preventative medication. I've heard of one dog that was imported to the US as a pup that was diagnosed with heartworm a year later, and recently an adult female that I sent to the US was also diagnosed with heartworm. This female was being given medication this year, but I'm not sure if it was continuous from when she was a pup.
Moral of the story? If you import from Japan, discuss with your vet about getting your dogs on heartworm medication. Even if the dogs were being given meds (like for instance the pups that were born at my kennel), they could get infected after receiving their monthly dose. Be aware, and beware the worm!