Gerard Houllier's long-term future at Villa has been called into question after his condition was revealed to be "serious".
The manager, who was admitted to hospital several days ago due to chest pains, underwent heart surgery in 2001 during his time at Liverpool. The same surgeon that operated on him then has been flown in from France to oversee his new treatment.
Villa director general Charles Krulak said: "He has suffered a problem that he has suffered before at Liverpool. It is serious, something that we need to be concerned about."
Krulak confirmed that Houllier would now be out for the rest of the season. Assistant manager Gary McAllister has taken over in the interim.