The 78-year-old emperor left the ICU in a wheelchair and was recovering well, according to the imperial household agency, while Jiji Press said he was reading books and newspapers.
Surgeons at University of Tokyo hospital carried out the operation - his first since he was treated in 2003 for prostate cancer - after tests showed a narrowing of two of his coronary arteries.
Doctors said after the four-hour operation that Akihito was in a stable condition and might be able return home in two weeks.
The surgery highlighted concerns about Akihito's health and has also raised questions about the rules of succession in the monarchy, which allows only males to become heirs, while women are forced to leave the household if they marry a commoner.
The five-year-old Prince Hisahito, the boy of Akihito's second son Akishino, is the only grandson of the ageing emperor.
The Japanese government plans to study a reform to the Imperial House Law so that women can remain as royal family members after marriage.