Emperor Akihito will undergo a coronary artery test Friday after a checkup found symptoms of cardiac ischemia, a condition caused by insufficient blood flow to the heart.
The symptoms were discovered Jan. 22 after the 77-year-old Emperor exercised during a routine examination at the University of Tokyo Hospital, the Imperial Household Agency said Wednesday.
"An announcement will be made after we receive the results of the test," an agency spokesman said.
The Emperor underwent surgery for prostate cancer at the same hospital in January 2003, during which his son, Crown Prince Naruhito, temporarily took over his official duties.
It was the first time an emperor left the palace grounds to be treated in a public hospital.
The Imperial Household Agency announced in December 2008 that the Emperor was in poor health due to stress, suffering from supraventricular arrhythmia, which can speed up the heart rate, as well as inflammation of the stomach and duodenum.
He is the 125th emperor, ascending the Chrysanthemum Throne on Jan. 7, 1989, after the death of his father, Emperor Hirohito, known posthumously as Emperor Showa.
He is married to Empress Michiko and has three children, Crown Prince Naruhito, Prince Akishino and Sayako Kuroda, who was a princess until she married a commoner.