The deaths of 67 heart surgery patients at a London hospital were probably, most likely, or definitely caused by "significant shortcomings" in treatment, a report has found.
The review looked at the cardiac surgery unit at St George's University Hospitals NHS Foundation Trust between 2013 and 2018.
Investigators found shortcomings in 102 of the 202 deaths they examined.
The hospital apologised for the "serious failings in care".
The Independent External Mortality Review was commissioned by NHS Improvement and looked into the cases of 202 patients who underwent heart surgery at the hospital in Tooting, south London.
A panel of medical and surgical experts found that there were "significant shortcomings" in the care of 102 patients and that for 67 of them, it either probably, most likely, or definitely contributed to their deaths.
In response to the report, the hospital's chief medical officer Dr Richard Jennings said the hospital "fully accepts the panel's findings, and we apologise unreservedly for the serious failings in care", adding it had fallen "way short of the high standards our patients deserved".
The Trust was found to have a higher mortality rate than other UK cardiac centres between April 2013 and March 2017, with a "toxic" row between surgeons thought to have contributed to it.
Dr Jennings said a Cardiac Surgery Task Force set up in 2017 to address issues had led to improvements in heart surgery mortality rates and they had been within the "expected range" since March 2018.
"The heart surgery service at St George's is now safe, and the current service is very different to the one the trust took urgent steps to improve in 2017," the chief medical officer said.
NHS Improvement said the report had been referred to the medical profession's regulator the General Medical Council (GMC) which would consider whether any regulatory action was required.