The heart has its own in-built protection system to prevent damage from heart attacks - and doctors are hoping to harness it.

It has been known for some years that a very minor heart attack triggers a natural response which greatly reduces the amount from subsequent attacks in the next few hours.

Some heart surgeons have even built the technique into their practice to aid the recovery of their patients.

However, scientists do not fully understand why or how this happens.

A team of researchers from Johns Hopkins University in Baltimore has found some clues to this natural protection system.

They hope that one day a drug might help protect those at risk of heart attacks - although this is still far from being developed.

The Johns Hopkins researchers found a protein on the surface of crucial cell components called mitochondria.

These are the cell's powerhouses, manufacturing the energy it needs to carry out its other functions.

Heart under stress

The protein, called mitoKCa, helps channel potassium into the mitochondria, where it appears to play an important role.

Previous research has already suggested that the uptake of potassium into the mitochondria is somehow important in the ability of the cell to stay alive when placed under extreme stress - such as that caused by a heart attack.

A chemical which "opened up" these channels appeared to help protect rabbit hearts against the the damage caused by an attack.

Dr Brian O'Rourke, who led the research, said: "If we can determine how mitochondrial ion channels regulate energy in heart cells, we may be able to protect the heart against life-threatening arrhythmias and other cardiac diseases."

'Step forward'

Dr Michael Shattock, a researcher in cardiac physiology at King's College London, said that other research had highlighted protein channels which appeared to have a similar function to that discovered by the Johns Hopkins team.

He said that it was far from certain that any drug which improved the way these worked would be able to help heart disease patients.

He told BBC News Online: "The problem is that we need to get to these people before they have their heart attack - we see most people after they have had one.

"This research is a step forward - the trouble is that this natural effect only lasts for a couple of hours after the minor attack."

The study was published in the journal Science.