Kyodo news agency, quoting the Imperial Household Agency, said the emperor, 78, would have the surgery on February 18.

Akihito had undergone an angiogram on Saturday which showed that blood vessels had narrowed over the past year. He had been treated in hospital for three weeks in November for cold, fever and symptoms of bronchitis.

The Imperial Household Agency was unavailable for comment.

Kyodo said the test was performed after the emperor experienced difficulty while engaging in light exercise.

Television footage on Sunday showed the emperor greeting doctors after being discharged from hospital following the examination.

Akihito had surgery for prostate cancer in 2003 and suffered stress-related health issues in late 2008, including irregular pulse and stomach bleeding. The following year, the royal agency said he would cut back on official duties such as speeches and meeting foreign dignitaries.

Akihito ascended to the throne after the death of his father Hirohito in 1989. He has spent much of the past two decades working to heal the wounds of a war waged across Asia in his father's name and helped bring the monarchy closer to ordinary citizens.

Having witnessed as a boy the rise of Japanese militarism and its defeat in 1945, the soft-spoken Akihito said he wanted to deepen international understanding through visits abroad, sometimes defying protests to do so.