Good question. I don't think you'd be refused care in an emergency, like an auto accident, or other life threatening event.
Health Care in Ontario for example, basically requires residence, and/or some sort of legal immigration or citizenship status. It's "universal", but it's certainly not free, as a large portion of our tax burden goes to pay for it, and most of our other Utopian social services. We are all issued a government photo Health Card, and must present it before any regular treatment or consultation begins.
Here's an FAQ list from the Ministry Of Health in Ontario.
http://www.health.gov.on.ca/en/public/p ... t.aspx#Q13
"Tourists, transients or visitors are not eligible for OHIP coverage."
OHIP is the Ontario Health Insurance Plan/Program, our government health care.
I would check with your current health care provider or insurer in the USA, and ask them what they
will cover for you in a foreign country. We do the same thing when we travel in America, and carry
additional emergency medical insurance.