Emperor Akihito visited the National Diet Library in Tokyo on Monday in his first official outing since he was hospitalized Friday for a heart checkup, the Imperial Household Agency said.

The 77-year-old Emperor, accompanied by Empress Michiko, viewed a digital archive system for old documents, including a handwritten encyclopedia of fish dating from the Edo Period from the early 17th to late 19th centuries.

The Emperor was diagnosed with arteriosclerosis in his cardiac blood vessels during the checkup at the University of Tokyo Hospital.