Retired Emperor Akihito was discharged from the University of Tokyo Hospital on May 10.

Accompanied by his wife Empress Emerita Michiko, he returned to their residence at the Akasaka Estate.

Officials of the Imperial Household Agency said the 91-year-old emperor emeritus was diagnosed with silent myocardial ischemia, a condition in which there are no symptoms but blood flow to the heart becomes insufficient when there is a certain amount of physical exertion.

He was admitted to the hospital four days earlier for examinations after showing signs of myocardial ischemia in a regular health checkup.

He was tested using electrocardiogram, X-ray, echocardiogram and CT scans of his coronary arteries.

The exams showed that his arteriosclerosis progressed during physical exercise, causing less blood flow to the heart.

Based on consultations with specialist doctors, Akihito will undergo additional drug treatment to suppress the progression of arteriosclerosis and improve blood flow.

The former monarch, who has regularly exercised and used the stairs to maintain muscle strength, will also avoid engaging in multiple physical activities simultaneously.

The officials said Emperor Naruhito, Empress Masako, Crown Prince Fumihito and Crown Princess Kiko have been informed about the diagnosis.