NHS Lothian has written to nearly 200 patients who have undergone heart surgery over the past six months to warn of a potentially fatal risk of infection.
The move took place after a review in which six operated patients had a heart valve infection.
NHS Lothian said it is believed that the infections may have been acquired during surgery and that "a number" of these patients died later,
However, the health department refused to report the number of deaths.
Health officials have now written to 186 patients undergoing surgery at Edinburgh's Royal Infirmary over the last six months to warn them of the potential risk of heart valve infection, called endocarditis.
The fungal infection can last up to six months and patients are informed about the symptoms.
As a precautionary measure, four operations scheduled for this week in the hospital were canceled to allow expert cleaning and disinfection of the theater.
A number of hospitals across Scotland have been causing infections that have led to the death of patients in recent months, including the Queen Elizabeth University Hospital in Glasgow, where a 10-year-old boy has been suffering from Cryptococcus infection associated with pigeon droppings ,
"We expect no further cases"
Professor Alex McMahon, Chief Anti-Infection Officer at NHS Lothian, said: "We sincerely wish to express sincere condolences to the relatives of the deceased patients, all of whom were informed at the time of their treatment that they were unusual in treating infections severely.
"Many patients receiving this type of surgery are already very ill and prone to infection, so we attach great importance to a rigorous infection prevention and control system."
He added: "We have contacted patients only as a precaution.
"Although this risk is very low and we do not expect any further cases, we know it can take up to six months for these infections to occur."
Endocarditis occurs in 0.5% of patients per year, and is usually the patient's own body.
Antibiotics-like medicines are available to treat the infection, but may have limited effect on very sick patients.
NHS Lothian reported that an incident management team was called after a case of endocarditis had been reported and they had reviewed the infection data of thousands of patients who had had many different types of surgery since the beginning of 2015.
The team found that six patients who underwent cardiothoracic surgery for 18 months were infected.
A number of these patients died later, but the board refused to say how many patients were for "patient confidentiality" reasons.
No cases were found before March 2017, and no cases have been reported in patients since November 2018.