A number of patients who had heart surgery died after contracting an infection during their operation, it has emerged.

NHS Lothian has issued a warning to 186 patients who have undergone heart aortic valve surgery since 2015 at Edinburgh Royal Infirmary to advise them of a possible infection risk.

It comes as the health board said six patients who required the surgery over 18 months were affected by unusual infections before some later died.

As a precaution, four planned surgeries have been cancelled this week to allow for specialist cleaning and disinfection of the theatres used for the procedure.

Enhanced infection control measures have also been put in place.

No cases were found prior to March 2017 and there have been no known issues in patients operated on since November 2018.

Professor Alex McMahon, NHS Lothian's executive lead for infection control, said: "We extend our sincere apologies and deepest condolences to the families of the patients who died, all of whom were informed at the time of their treatment that they had an unusual and difficult to treat infection."

He admitted it was a "worrying time" for those who had received letters but reiterated the move was a precaution.

"We know this will be a worrying time for those who have received letters but we have contacted patients purely as a precaution," he said.

"The risk is very low and we do not anticipate any more cases, however we know that it can take up to six months for these infections to materialise.

"We want to make sure those patients know what symptoms to be aware of and to contact NHS Inform if they have any concerns.

"Many patients receiving this type of surgery are already very ill and vulnerable to infection so we place the highest importance on a stringent infection prevention and control regime.

"We are very sorry for the inconvenience and disappointment caused to the patients who have had their procedures cancelled this week but we must prioritise patient safety above all else. All those affected will be given new appointments as soon as possible."