YOu need to ask hospital for

some information about Public Aid(it may have a different name in your state). In some democrate state such as california, if your parents (as foreigners visiting U.S. now) are over 65 (senior) and have a real emergency and you cannot afford to pay the bill, the state may cover all the bills so you won't need to pay anything. But you need to see the related documents and find out if you are eligible to apply for it. For example. your yearly income, your parents' age and their medical condition. But for some republic states, there is no such policies so you have to pay everything.
I heard of a guy's father has a heart attack while visiting them in California, and the state not only paid everything, but also paid for his bypass surgery.
He has no insurance in U.S. and 65 years old. His son's yearly income is high also but he have two childern of their own. So, even you has a nice income, you may still apply for it if your state allows.