United Continental CEO Oscar Munoz is "recovering well" after undergoing heart transplant surgery Wednesday morning.

The airline company issued an update about Munoz's health status on Thursday that included statements from his medical team.

His doctors "expect a quick recovery and return to his duties as CEO," said Patrick M. McCarthy, the chief of cardiac surgery for Northwestern Medicine.

Munoz, 57, has been sidelined since suffering a heart attack in October. The company says he's expected back at work this spring.

Munoz came to United's C-Suite at United from outside the company. He replaced Jeff Smisek, who was forced to resign amid a federal probe into whether the company rigged flight schedules to curry favor with the New York-New Jersey Port Authority. The incident is part of an ongoing federal investigation.

United's general counsel, Brett Hart, was named the temporary CEO on Oct. 19, 2015 and has been filling in until Munoz is healthy enough to return.

United (UAL) revealed Thursday that Munoz "had been cleared to return to work prior to the transplant," and had been improving with the help of an implanted medical device.

He'd even begun to "gradually resume company-related activities," United said, but that a heart transplant was the "preferable" course of treatment for the long term.

Dr. Jon Kobashigawa, Cedars-Sinai Heart Institute's director of heart transplants, told CNNMoney on Wednesday that patients can recover quickly after a successful transplant.

"They're up and around after two, three, four days," Kobashigawa said. He added that a patient can be back to running on a treadmill in as little as six weeks.

The waiting list for a donor heart contained about 4,200 names as of Jan. 1, according to the United Network for Organ Sharing.

When an organ becomes available, patients are selected based on medical urgency along with other factors including blood type and body size, according to UNOS.