Researchers have shown cardiac surgeons can save a significant amount of precious donated blood and still safely perform life-saving heart surgery.

A major international study has found cardiac surgeons can safely use significantly less blood in heart operations.

Cardiac surgery relies heavily on donated blood because of the high blood transfusion rates, but researchers say using less blood would represent a significant cost saving to health systems and ease the burden on blood donations services.

"Anywhere from about 25 to 70 per cent of patients having cardiac surgery will require a blood transfusion," said Dr David Mazer at the University of Toronto who led the Transfusion Triggers in Cardiac Surgery Trial (TRICS-III).

But there are potential risks to blood transfusion, and clinicians have become more cautious about transfusing large amounts of allogenic (donor) blood, he explained.

"Blood generally is quite safe these days, so people shouldn't be afraid of receiving a transfusion of allogenic blood if their clinicians deem that it is appropriate to do so, however, there are still risks," Dr Mazer said.

"We did this study to establish the safety of restrictive transfusion and to document its effect on patient outcomes and on saving of blood and money," Dr Mazer told AAP.

The five-year clinical trial, published in the New England Journal of Medicine, monitored patients at 73 institutions across 19 countries, including Australia.

The Australian arm of the study involved more than 620 patients across 12 hospitals in Victoria, New South Wales and South Australia.

On average, one or two units of blood was safely saved each patient using restricted transfusion, the study showed, which Dr Mazer said represented significant financial savings of around $US3 million "just for the patients who were in our study".

In Australia, the current listed cost per unit of blood is $AU412, on top of which are hospital costs that can take the total cost of a transfusion up to as much as $AU1,000 per unit.

Dr Mazer presented the findings at the 27th Annual Congress of the Association of Thoracic and Cardiovascular Surgeons of Asia in Melbourne.

Professor Alistair Royse at Melbourne University says while the study was extremely successful, more research is needed to analyse the extent of the potential cost saving across Australia's health system.

"This study may significantly change clinical practice across the globe by supporting the ongoing trend towards using less blood transfusions at a lower haemoglobin concentration," Professor Royse said.