Bristol Children's Hospital is to reduce the number of heart operations carried out after a formal warning over staffing levels on its cardiac unit.
It follows complaints by parents and a spot inspection by the regulator, the Care Quality Commission.
Inspectors found there weren't enough qualified, skilled or experienced staff and patients were being put at risk.
Six families are currently pursuing legal action against the hospital's trust after their children underwent heart surgery at the hospital.
Our health correspondent Rebecca Broxton reports: