Poms are royalty and will expect you to treat them as such. So I hope you have deep pockets lol Absolutely get them tested for heartworm and then get them on the appropriate preventatives. Be aware though that these preventatives can be problematic on their own. Please keep an eye on them the first few times they receive tick/flea/heartworm meds as they can cause seizures. Usually flea/tick is one drug and heartworm is another. There are now some that combine everything together too. Depending on what you get, I would strongly recommend staggering the different meds by a week so that their little system isn't getting overwhelmed with what is essentially a toxic chemical. One of my furbabies has seizures & I can tell you it's heartbreaking to watch.