Mr Charles Haughey has been moved to the coronary care unit of Beaumont Hospital in Dublin where his condition is described as comfortable and stable.
A hospital spokeswoman said Mr Haughey had spent the night in intensive care and after he was assessed by his medical team the decision was made to move him to coronary care.
He was rushed to hospital yesterday after collapsing at his Co Dublin home.
The former Taoiseach was said to have a "serious life-threatening cardiac condition" and had been sedated to allow ventilation.
He was later taken off the ventilator and was able to sit up in bed yesterday evening and talk to his wife, Maureen, and his children.
Mr Haughey's son Seán said earlier reports his father had suffered a heart attack were incorrect. Instead he was believed to have suffered from ventricular defibrillation, a condition in which the lower chambers of the heart function irregularly.
Séan said his father was "out of danger", and in good form. He added that the family were very happy with his progress.
The general manager of Beaumont Hospital said Mr Haughey's condition would be monitored closely over the next day or so.