A North Shore Hospital nurse with an "unblemished record" has been stood down after a 60-year-old grandmother died when she was given 10 times too much heart medication.

Shirley Curtis, who had earlier had a triple bypass operation, was admitted to North Shore Hospital with breathing problems and swollen feet just before Easter.

She was treated for five days and was due to be discharged.

But she received 10 times the prescribed dose of metaprolol, a beta blocker which slows the heart.

"Things were going off and red lights were flashing and they said they can't get a pulse and I just burst into tears," niece Donna Stanton told One News.

"We were told that the doctor had prescribed 12.5ml and the nurse had given her 125ml, which caused severe heart failure and then multiple organ failure."

The family were told Ms Curtis was not going to survive, and she died the next day.

"We don't want this to happen to anyone else," Ms Stanton said.

"We are not a Third World country. Our medical system should be better."

Waitemata District Health Board chief medical officer Andrew Brant told the Herald last night that the hospital was extremely sorry.

"The nurse and the staff are all completely shattered and devastated."

The nurse in question had been stood down while the investigation was conducted, Dr Brant said.

The health board chairman, Dr Lester Levy, said the accident came down to human error.

"It's a coroner's case and a police investigation and we're doing our own investigation," he said.

"But it's very disappointing, it's frustrating and it's tragic. In this case it was an experienced nurse, a good nurse with an unblemished record ... This is an inexplicable medical error that had tragic consequences."

Dr Levy said the hospital's most senior clinicians, the director of nursing and Dr Brant had interviewed the nurse, the clinicians and the pharmacists involved in the incident.

"We'll be questioning everyone involved, looking at what was written in the note, what was written in the chart, what was discussed in the handover of patients and what were the circumstances at the time - we want to find the root error."

Dr Levy said the health board had implemented a programme called First Do No Harm to try to reduce errors and to resolve issues it had had previously.

"There's been a lot of issues that have happened with us in the past about poor emergency department, poor systems, poor staff," he said.

"But all of those things have now changed."

Dr Levy said medical mistakes could be made by hospital staff for various reasons.

"Sometimes the script wasn't written properly, or it wasn't clear ... Other times there's a breakdown in communication. Neither of these was the case this time. This was just an unfortunate, tragic, human error made by a very experienced nurse ... These things happen," he said.

Detective Senior Sergeant Kim Libby said police were investigating the death but it was a "routine coronial inquiry on behalf of the coroner" and was unlikely to turn into a criminal case.

April 2011: Shirley Curtis dies after being given an overdose of heart medication.

August 2010: Brendon Parrish, 37, dies of a heart attack after appendix surgery. His brother, Darryl, criticised the hospital, but clinicians said the care was appropriate.

Sept 2010: Herald contacted by a number of patients complaining about inadequate care and delays in receiving treatment.

2007: Care of five patients compromised by inadequate systems and the failure of the district health board to resolve overcrowding and staff shortages.