Japan's Imperial Household Agency says Emperor Emeritus Akihito has been diagnosed with heart failure, but that his condition is improving with treatment.

The agency says the Emperor Emeritus, the father of Emperor Naruhito, underwent an MRI scan at the University of Tokyo Hospital on Sunday.

Doctors detected a faulty valve on the right side of his heart.

Heart failure was suspected based on several medical evaluations conducted since last month.

The agency says he doesn't feel the effects of the disease, and that his condition is improving since he started taking medication and restricting his fluid intake in late June.

In 2012, the Emperor Emeritus underwent a heart bypass operation after being diagnosed with angina. But his doctors say there's no link between that operation and his current condition.

The agency says for now the Emperor Emeritus has reduced his activities, such as by shortening his morning and evening walks, but that other restrictions aren't necessary. The agency says he will continue to receive treatment at home.

The agency also says his wife, Empress Emerita Michiko, underwent an outpatient operation on her right eye on Sunday. She previously had cataract surgery on the same eye. The agency says she is making a good recovery.