Emperor Akihito has been diagnosed with arteriosclerosis and will be put on medication, the Imperial Household Agency said.
The stiffening of the 77-year-old Emperor's cardiac arteries was discovered through a contrast agent administered during a medical checkup Friday at the University of Tokyo Hospital, the agency said.
The Emperor stayed at the hospital overnight and returned to the Imperial Palace on Saturday, the agency said, adding he is expected to carry on with his normal duties and activities.
He will be allowed to engage in exercise, like tennis and walking, according to Ichiro Kanazawa, the Imperial household medical supervisor.