He reportedly collapsed at the Brasserie 8½ restaurant in Manhattan before being rushed to a hospital for emergency surgery, according to Adrian Wojnarowski of ESPN. A 911 call was made for cardiac arrest, via Morena Basteiro of ABC7.
Stern served as the league's commissioner from 1984 until retiring in 2014, when he was replaced by Adam Silver.
The 77-year-old was a major part of the sport's expansion over the past few decades, and he was inducted into the Naismith Memorial Basketball Hall of Fame in 2014.
Stern has continued to follow basketball since stepping down as commissioner, recently discussing the league's drug policy, as well as its handling of China.
He has also invested in several startups and hopes to improve the viewer experience for games.
"Our thoughts and prayers are with David and his family," Silver said in the statement.