Veteran broadcaster Paul Holmes is in an induced coma.
Mr Holmes had been in a stable condition while recovering from successful open-heart surgery on Wednesday, when a team of surgeons worked for four hours to remove a blockage and carry out remedial work on his heart.
The 62-year-old was diagnosed with hypertrophic cardiomyopathy, a usually genetic condition in which the heart muscle thickens and impedes and blocks blood flow. It affects about one in 1000 people.
Before the operation he admitted feeling anxious and "a bit scared'', but he and wife Deborah were buoyed by good wishes from family and supporters.
Prior to surgery, Mr Holmes said he had been feeling breathless and lacking energy for about a month, which he thought were a result of being rundown after finishing writing a book.
When his condition was confirmed by his Hastings cardiologist Richard Luke he was rushed to Auckland Hospital by helicopter on May 30.
Mr Holmes has been positive about his long-term prognosis, including a return to work as a Newstalk ZB and TVNZ host and Weekend Herald columnist, saying he had confidence in the surgeons.
During his life he has has survived a road accident crash, a helicopter crash and cancer.