Japanese Emperor Akihito has undergone a successful heart bypass operation.

National network NHK said the surgery at the University of Tokyo Hospital on Saturday lasted about five hours.

The Imperial Household Agency said a medical team from the University of Tokyo Hospital, joined by another team from Juntendo University Hospital, performed the procedure on the 78-year-old emperor.

The surgery was scheduled after tests last week showed that Mr. Akihito's heart condition had worsened over the past year.