United Airlines CEO Oscar Munoz received a heart transplant Wednesday and is recovering.
The airline expects him to return to his position at the end of the first quarter or start of the second quarter. United said the procedure was "the preferred treatment" for Munoz, who had a heart attack in October.
United named Brett Hart its acting chief executive in October. Munoz was initially named CEO in September.
Shares of the airline's parent company, United Continental Holdings, fell about half a percent in extended trading Wednesday. The stock rose modestly in regular trading.