United Airlines confirmed that the newly appointed CEO Oscar Muñoz has suffered from a heart attack on Thursday and is now in an indefinite medical leave.

As a result, the airline company has decided to name Brett Hart as the acting CEO in the absence of Muñoz. The appointment is said to be effective immediately.

Prior to Hart's appointment, the company was indecisive on whether it would be best to appoint an interim CEO or to find a new one.

"The company anticipates it will today conclude the corporate governance process necessitated by the hospitalization of President and CEO Oscar Muñoz," said Chairman Henry L. Meyer III in a statement. "The company expects to release more details either later today or tomorrow. In the meantime, the United family's thoughts and well-wishes are with Oscar."

It was on Sept. 8 when Muñoz became the new CEO of United Airlines. Upon assuming his post, Muñoz has pledged to make a number of radical changes that include enhancing operations and employee relationship as well as regaining the trust and satisfaction of customers.

"We are committed to re-earning your trust," said Muñoz. "We want to be the first choice for every trip you take. We need to do the small things well. We have to deliver meaningful, everyday improvements."

Brett Hart, Muñoz's replacement, will work closely with Meyer, according to United. Prior to being an interim CEO, Hart was the airline's executive VP and general counsel. He has been with United Airlines since 2010 and has been responsible for the company's regulatory affairs, food services, contact centers, community affairs and corporate security.

"I am confident in his ability to continue to implement the company's strategy and Oscar's mission of bringing United's people together around the shared purpose of becoming the best airline for our customers and employees," said Meyer in a statement.

Prior to joining United, Hart was also connected with Sara Lee as its executive VP and general counsel. He became a partner at Sonnenschein Nath & Rosenthal and also served as a special assistant to the general counsel at the Treasury Department.

"We believe strongly that we can continue to make steady progress on increasing shareholder value by working together to deliver a great product to our customers," said Hart in a statement.