Charles Haughey is expected to be moved out of the intensive care unit at Dublin's Beaumont Hospital today.
The former Taoiseach regained consciousness last night and was taken off a ventilator machine.
His condition was still critical but stable, although his son Sean revealed that his father had not suffered a heart attack.
Instead, a statement from the hospital said that Mr Haughey had a life-threatening cardiac condition, amounting to an irregularity of the heart.
Mr Haughey was rushed to hospital in the early hours of yesterday morning after he collapsed at his Dublin home.
The 75-year-old, who resigned as Taoiseach in 1992, was diagnosed with prostate cancer in 1995.
Because of his illness, he has been giving evidence in private to the Moriarty Tribunal over the last few weeks.