"You were born with a number of heart cells and if you damaged them during life, that was it, you could never replace them, unlike skin, which regenerates when you injure it.

"But in the last five years there's been the discovery of cells in the heart that sit around and only get activated if there's an injury to the heart. So that's given the notion that stem cells could in fact grow new heart muscle. Scientists are starting to inject stem cells into hearts at times of heart attacks."

Professor Garry Jennings, at the Baker Institute, says it is a "whole new paradigm" for heart researchers.

"Now we know there are little colonies of natural stem cells in heart muscle. They're not there to repair the catastrophic damage of a heart attack. In fact they're probably left over from evolution. But what we've got to do is find some way of turning them on; find what the switches are."

There is a lot of interest in whether the heart has its own stem cells that could be recruited to repair cells, says #Associate Professor Diane Fatkin, of the Victor Chang Institute, but "there's still a lot of uncertainty about whether these cells exist in the heart and what they do".

Such cells within the heart might not be enough for replenishment, she says, giving rise to research into whether stem cells taken from bone marrow or embryos could promote regeneration if injected into the heart.

"There's a lot of hype and a lot of promise, and a long way to go before we've sorted out the whole stem cell story," Fatkin insists.

Professor Bob Graham, of the Victor Chang Institute, is spearheading a study with St Vincent's Hospital that gives stem cells and other factors that might mobilise the cells to patients with severe chronic angina due to coronary artery disease who have exhausted other available medical and surgical options.

The results of the first small phase of the study, examining safety, are being published by by the American Heart Journal . "It's looking promising in terms of safety," says Fatkin.

"The big thing that raises sensitivities is the use of embryonic stem cells. St Vincent's is a Catholic hospital, so we don't do embryonic research. I think there's general appreciation that looking at adult, fully matured, stem cells, particularly if they're from the same patient, from their bone marrow, doesn't have the same ethical considerations as the use of embryonic stem cells. We really don't know that embryonic stem cells are really going to be any better than any other types of stem cells."

But Jennings says it is unresolved whether in the heart adult stem cells from bone marrow or embryonic stem cells would be most effective.

"Given the embryonic stem cell lines that have been generated come from cells that will be discarded anyway, I think you'll find most biological scientists would support their availability for research, at least at this point."