A free card that gives you access to necessary medical attention.  It is state-provided healthcare during a temporary stay in any of the 28 EU countries, Iceland, Lichtenstein, Norway and Switzerland, under the same conditions and at the same cost (free in some countries) as people insured in that country.

Cards are issued by your national health insurance provider.

Important: the European Health Insurance Card

• is not an alternative to travel insurance. It does not cover any private healthcare or costs such as a return flight to your home country or lost/stolen property.
• does not cover your costs if you are travelling for the express purpose of obtaining medical treatment.
• does not guarantee free services. As each country's healthcare system is different, services that cost nothing at home might not be free in another country.

http://ec.europa.eu/social/main.jsp?catId=559