Michael Lohan -- Back in the Hospital for Chest Pains

Michael Lohan was taken to the hospital early Friday morning after experiencing chest pains ... TMZ has learned.

According to our sources, Lohan was transferred from a rehab facility in Palm Beach, FL. We're told doctors found more blood clots and put him on medication to try and break them up.

Our sources say doctors feel they don't need to perform surgery, but they want to keep in the hospital for a couple of days to make sure the medication works.

This is the second time in two months Lohan has been hospitalized for heart problems. He had surgery to repair a blockage back on December 5.