Japan Emperor Akihito's heart bypass surgery that lasted about five hours ended successfully Saturday, national network NHK and other media said.
The 78-year-old emperor was advised to undergo the procedure after tests showed a narrowing of two of his coronary arteries.
The Imperial Household Agency declined to immediately confirm the reports of the successful operation.
His doctors were scheduled to hold a press conference from 6.00 pm (0900 GMT).
The emperor went into the operating theatre at the University of Tokyo Hospital at 9.24 am (0024 GMT) and the surgery lasted more than five hours.
The aim of the procedure was "to maintain and to improve his majesty's daily life", a palace spokesman said earlier.