The American Heart Association certification lasts 2 years. The certification for the Red Cross lasts a year. In either case you are covered by the good samaritan laws if you act in good faith.

Edit:
It is a case of time. I am woefully out of date with it. I work with an elderly population, and have had to help a person that was having a heart attack. Luckily, they were conscious- to no CPR.

You have reminded me that I need to get our entire office certified.