A new device that preserves hearts after people have died could dramatically increase the number of organs that can be donated, according to its inventor.

The technique, developed at Melbourne's Alfred Hospital, uses a device about the size of a bar fridge that keeps donor hearts healthy by pumping a solution of oxygen and nutrients through it to flush out waste.

The process keeps the cells of the heart healthy so the organ can be resuscitated when it is put into the recipient.

The process can keep a heart alive for up to 12 hours - three times longer than the current method of putting hearts in plastic bags inside an esky full of ice.

Hospital spokesman Professor Frank Rosenfeldt said the extra time meant more patients in need of a heart transplant would have access to organs.

"About a third to three quarters of hearts that are offered for transplant can't be used for one reason or another," he said.

"One reason is that they're too far away and the time period will be too long before they can be transplanted."

The technique allows hearts to be taken from what are known as "marginal donors", generally older patients or donors with hearts that are not considered to be strong.

Professor Rosenfeldt said hearts that have stopped beating may also become available for transplants.

"A normal donor is a brain-dead donor where the heart is actually beating just before it's removed in the operating theatre," he said.

"But donation after circulatory death is where the heart has actually stopped.

"Provided we obtain the heart within 30 minutes we can obtain the heart and start resuscitating and preserve it with this new technique."

Professor Rosenfeldt said 30 per cent more hearts could be used in transplants using the device.