Lee, 72, is largely credited with turning Samsung -- founded by his father in 1938 -- into a global brand which is now the world's top chip and smartphone maker.
He is also the de facto head of the entire business empire, which employs some 200,000 staff in dozens of affiliates and dominates many aspects of life in South Korea.
Recent health problems have led Lee to be less involved in the day-to-day running of the giant conglomerate than before -- although he still has a major say in important strategic decisions.
He was hospitalised late Saturday and underwent a surgical procedure to widen his arteries the next day.
Samsung officials said he was breathing without assistance on Monday and was in a "stable" condition.
"There has been no disruption in the group's day-to-day operation," a group official told AFP.
AFP