Scientists at University of Bristol have found that "master" cells from veins left over from lifesaving bypass surgery may help treat future heart problems.
The researchers extracted stem cells from the veins, then used them to stimulate new blood vessel growth in mice, according to reports in Circulation.
The researchers have claimed that their findings could bring treatments to repair damaged heart muscle one step closer.
However, a stem cell expert warned that they remained some years away.
The latest discovery uses a "waste" product from thousands of operations carried out on heart patients each year.
In a heart bypass operation, the surgeon takes a section of vein, usually from the patient's leg, and uses it to replace a blocked or narrowed section of heart artery.
Normally, they select a slightly longer section than is actually required.
In the study, the researchers took the leftover piece and, in the laboratory, they managed to extract "progenitor" cells from the veins and persuade them to increase in number.
When the stem cells were injected into the leg muscle of a mouse, which had been deprived of blood to simulate conditions in a damaged heart, the cells appeared to trigger the development of new blood vessels and improve blood flow.
"This is the first time that anyone has been able to extract stem cells from sections of vein left over from heart bypass operations," the BBC quoted professor Paolo Madeddu, who led the research.
"These cells might make it possible for a person having a bypass to also receive a heart treatment using their body's own stem cells."
However, other experts said much more work would be needed before such cells could be used widely in humans.