Emperor Emeritus Akihito was confirmed Friday to be suffering from supraventricular arrhythmia, according to an aide.

The 91-year-old former emperor was discharged from the University of Tokyo Hospital the same day, after he began receiving an additional oral treatment for his heart during his hospitalization.

He will refrain from exercise that is strenuous for the heart, including taking stairs.

Emperor Emeritus Akihito, accompanied by Empress Emerita Michiko, 90, left the hospital in Tokyo's Bunkyo Ward by car at around 11:30 a.m. and returned to the Sento Imperial Residence in Minato Ward.

He began taking the oral medication to ease the load on his heart from asymptomatic myocardial ischemia, which was identified this May. The treatment did not cause any major side effects.

Still, a pre-medication test revealed that the former emperor had supraventricular arrhythmia, characterized by a rapid pulse. The new medication is expected to be effective against this condition as well.

Doctors will monitor his progress closely. His walks will be shortened in duration and distance, although he will continue his research on goby fish at the biological research institute in the Imperial Palace.

Whether the emperor emeritus will go on his usual summer retreat will be determined by his recovery.

In 2022, the emperor emeritus was diagnosed with right heart failure caused by tricuspid valve insufficiency.

He was admitted to the university hospital in May this year for a heart examination and also diagnosed with asymptomatic myocardial ischemia. After being discharged from the hospital, he was treated with medication to improve blood flow.

As there was no improvement, however, the medical team determined that he needed the additional oral medication to ease the strain on his heart.

The former emperor had been hospitalized since Monday for dosage adjustments. The empress emerita visited him every day during the hospitalization.