The surgery was performed because MM Lee has been experiencing symptoms of cardiac arrhythmia - irregular heart rhythm - which showed up with his atrial flutter on Sept 14.

'He is recovering from the surgery and is expected to be discharged from the hospital on Monday,' said the statement.

MM Lee will still go ahead with his trip to Hong Kong from Monday to Wednesday to have a dialogue session with former President Bill Clinton at his Clinton Global Initiative (CGI) Asia Meeting, accompanied by his doctors.

Atrial flutter is not uncommon among people of his age.

Even when he was warded for an abnormal heart rhythm in September, MM Lee still kept his date with the Global UBS Philanthropy on Forum on Sept 13 night , addressing the 200 participants at the Arts House via video link.

He was discharged a day later.

Mr Lee, who had two operations in 1996 to clear a blocked heart artery, is known to exercise regularly.