MESA, Ariz. — Chicago Cubs second baseman Mark DeRosa remained hospitalized today, one day after complaining of a rapid heartbeat during fielding drills.

The team initially said DeRosa was released yesterday evening, but said today that he was kept overnight at Banner Desert Medical Center in Mesa as a precaution.

DeRosa is expected to be examined by a cardiologist tomorrow and could be back on the field by the middle of the week, the Cubs said.

His irregular heartbeat was not life-threatening, according to the team.

"He had an episode yesterday of an atrial dysrhythmia that he's had in the past that has lasted briefly," team doctor Stephen Adams said, speaking with reporters Sunday afternoon at DeRosa's request. "This one had a bit of an extended period of time for which he contacted our head athletic trainer, Mark O'Neal, who appropriately saw him and was with him."

Adams said DeRosa, who turns 33 on Tuesday, is undergoing an evaluation.

DeRosa batted .293 with 10 home runs and 72 RBIs in 149 games for the Cubs last season. They signed him to a $13 million, three-year contract in November 2006.

He began his major league career with Atlanta in 1998. DeRosa also played for the Texas Rangers in 2005 and 2006.