Wales' largest hospital says it has solved a problem with sterilising equipment that delayed operations.
Cardiff and Vale University Health Board (LHB) said 19 operations, mainly cardiac surgery, were postponed at the University Hospital of Wales.
It said there were a "limited number of quality control issues" in the sterilisation of surgical tools.
Other LHBs are helping to sterilise equipment while the hospital's sterile services unit is refurbished.
BBC Wales has been contacted by one family concerned that a relative's urgent operation was cancelled due to the problem.
The surgery was due to take place on Wednesday to treat a serious, progressive, illness.
The family have not been given a date for the operation and say they fear that further delay will endanger the patient's wellbeing.
They have made an official complaint to the local health board.
Dr Graham Shortland, the LHB's interim medical director, said: "We would like to reassure the public that the safety of patients is our main priority.
"There have been a limited number of quality control issues which have led the health board to postpone a small number of surgical procedures, mainly in cardiac surgery.
Dr Shortland added: "We understand that such postponements can be distressing for patients and their families but would like to reiterate that the safety of patients is paramount."
The LHB said normal elective operations would resume on Monday.