Japan's Emperor Akihito is in a stable condition after heart bypass surgery that went as planned, doctors say.
The 78-year-old head of state's surgery lasted just over five hours at the University of Tokyo Hospital.
One of the three surgeons, Minoru Ono, told a news conference the operation went smoothly.
"We confirmed a sufficient blood flow back in the arteries," he said.
Another surgeon, Atsushi Amano, said it was too early to talk confidently of the operation's success, saying it would be "measured by whether the emperor can regain the normal lifestyle he had wished for".
The emperor, who ascended the throne in 1989, has suffered from poor health in recent months, the BBC reports.
Doctors decided to carry out the operation after tests earlier this month showed his heart condition had worsened since a year ago. The tests showed a narrowing of two of his coronary arteries.
Emperor Akihito plays a largely ceremonial role but is deeply respected by many Japanese.
The emperor is likely to be discharged after about two weeks if he recovers well from the operation.