What would cause a cylinder 3 misfire on a 2007 Chevy HHR?

[hokiedokie24]

I had an engine service light come on my 2007 Chevrolet HHR and it stayed on for a little while but went off. I had it checked at Advanced Auto and it said it was a cylinder 3 misfire. What are the possible causes for this?? Again, the light is now off.