Last year, round about this time Mark DeRosa had the same issue with the irregular heartbeat.
February 24, 2008, Mark DeRosa was rushed by ambulance to the hospital and spent the night, resulting in his being held out for a few days. Of course DeRosa had a good season last year, and...
"The Cubs stress they’ve been informed at this point there are no long-term concerns about DeRosa’s condition or playing status."
Hampton, obviously wasn't rushed to the hospital, so this doesn't appear to be as serious.