The Japanese Emperor's uncle, Prince Mikasa, will undergo surgery to repair a faulty heart valve as early as Wednesday.
The 96-year-old prince reported feeling something wrong with his chest at the funeral of his son, Prince Tomohito of Mikasa, last month. The prince was hospitalized the next day.
The prince's heart condition deteriorated and his blood pressure fell to 50 at one time. Doctors say one of his heart valves is failing to function properly and that he also suffers from kidney malfunction.
Doctors are concerned the planned surgery will place a significant burden on the body of the prince. It requires general anesthesia and an artificial heart-and-lung machine and will last several hours.
They say they will carefully monitor the Prince's condition during surgery.
The prince is a younger brother of the late Emperor Showa.