The 69-year-old had been in "extremely critical” condition before undergoing the surgery in Vienna on Thursday.  Head of the Department of Thoracic Surgery Walter Klepetko, who performed Lauda's surgery had words of optimism the day after the procedure.

"In the last seven days, Mr. Lauda was kept alive only by a pump," Klepetko said in a television interview on Austria's Oe24 on Friday. Reports also suggested the triple world champion had been brought out of a medically-induced coma.

"Without a transplant, life expectancy in such circumstances would be limited to days or weeks. Considering the not very easy circumstances we are very, very happy with the developments," Klepetko added."Breathing on his own will begin in the next few days, but there's no rush."

The hospital are due to release a comprehensive update about Lauda's condition at a later time.

jt/(reuters, dpa)