Cluster of never events at Royal Cornwall Hospital
BBCA hospital trust had a cluster of "never events" since coming out of special measures earlier this year.
In one incident a heart patient had a 39cm (15in) piece of wire left in them after a procedure at the Royal Cornwall Hospital in Truro (RCHT).
The trust has recorded eight never events since April, having had none in the previous 13 months.
A never event is a serious incident that is entirely preventable.
In a statement RCHT said: "We are very disappointed that we have had never events after 13 months of not having one.
"Whilst none of the never events resulted in long term harm to patients, it is absolutely right that we are open and transparent about them, particularly where they could suggest a need for national changes in practice".
On 1 May a section of guide wire broke off from a 190cm (75in) wire and this was not detected after a cardiology procedure to insert a stent.
Following an investigation, processes were changed to ensure that "wire and catheter counts and integrity checks must be carried out" at the end of procedures, the trust said.
Other never events included three dermatology procedures where patients had the wrong lesions or moles removed.
A review found the safety checklist had not been followed in these incidents.
Other cases included a swab being retained after breast surgery, and an incorrectly sized lens being inserted during cataract surgery.
RCHT was taken out of special measures in February, but is still placed within the 'requires improvement' category by the Care Quality Commission.