FYI:

Is there a legal risk to performing CPR?

Virtually all 50 states have enacted laws to protect people who render aid in an emergency from liability. These laws are often termed “GOOD SAMARITAN LAWS.” These laws are intended to encourage people to render aid in emergencies without the fear of litigious consequences. Good Samaritan laws generally provide that people who render aid at the scene of an emergency will not be liable for civil damages if they act in good faith.

http://www.cpr-professionals.com/aboutus.html

I think that getting training and a certification may be necessary for the protections of that law to apply.

In California, you do need training and certification:

http://www.swc.cc.ca.us/~kjacobs/goodsam.htm