A woman died after surgeons inserted a heart valve upside down.
Sheila Hynes suffered massive internal bleeding during what should have been a routine operation at the Freeman Hospital in Newcastle upon Tyne.
The 71-year-old great-grandmother never came round from the operation after the mistake caused irreversible damage to her heart.
Newcastle Upon Tyne Hospitals NHS Foundation Trust has admitted the error.
Mrs Hynes died a week after the operation, having never recovered consciousness.
The family have begun legal action. Their lawyer, Nicola Evans, said she believes Mrs Hynes’ right to life under the Human Rights Act was breached.
Mrs Hynes’ daughter, Jan Hopper, 55, from Haltwhistle in Northumberland, said: “My life has been destroyed by what happened to my mother.
“My mother was the picture of health that week and I can remember saying to her ‘mum, you look absolutely stunning’.”
An inquest into the April 2015 death has been scheduled for later this year.
Mrs Hynes, a widow with seven grandchildren and eight great-grandchildren, had undergone the surgery to try to improve her breathing, which was being hampered by inadequate blood flow.
Mrs Hopper said staff told her there had been a complication, but it was not until three days after the operation that the family were informed an error had been made.
She said: “We were told that putting the heart valve on the wrong way had caused her heart to balloon up and expand, and when it contracted the wall of her heart was pierced on an instrument.
“We still haven’t come to terms with what happened. It has been traumatic.”
The trust has admitted full breach of duty and that the error which caused Mrs Hynes’ death was the insertion of the heart valve the wrong way.
A trust statement said: “Our thoughts are with Mrs Hynes’ family at this difficult time and we would like again to offer our sincere condolences to them.”
The trust said an investigation had been carried out but it could not comment further before the inquest.
Sheila Hynes died when surgeons inserted heart valve upside down