SAN FRANCISCO – Stem cells grown from patients’ own cardiac tissue can heal damage once thought to be permanent after a heart attack, according to a study that suggests the experimental approach may one day help stave off heart failure.

In a trial of 25 heart attack patients, 17 who got the stem cell treatment showed a 50 percent reduction in cardiac scar tissue compared with no improvement for the eight who received standard care. The results, from the first of three sets of clinical trials generally needed for regulatory approval, were published Tuesday in the medical journal Lancet.

“The findings in this paper are encouraging,” said Deepak Srivastava, director of the San Francisco-based Gladstone Institute of Cardiovascular Disease. “There’s a dire need for new therapies for people with heart failure, it’s still the No. 1 cause of death in men and women.”

The study, by researchers from Cedars-Sinai Heart Institute in Los Angeles and Johns Hopkins University in Baltimore, tested the approach in patients who recently suffered a heart attack, with the goal that repairing the damage might help stave off failure. While patients getting the stem cells showed no more improvement in heart function than those who didn’t get the experimental therapy, the theory is that new tissue regenerated by the stem cells can strengthen the heart, said Eduardo Marban, the study’s lead author.

“What our trial was designed to do is to reverse the injury once it’s happened,” said Marban, director of Cedars-Sinai Heart Institute. “The quantitative outcome that we had in this paper is to shift patients from a high-risk group to a low-risk group.”

The stem cells were implanted within five weeks after patients suffered heart attacks. Doctors removed heart tissue, about the size of half a raisin, using a minimally invasive procedure that involved a thin needle threaded through the veins. After cultivating the stem cells from the tissue, doctors reinserted them using a second minimally invasive procedure. Patients got 12.5 million cells to 25 million cells.

A year after the procedure, six patients in the stem cell group had serious side effects, including a heart attack, chest pain, a coronary bypass, implantation of a defibrillator and two other events unrelated to the heart. One patient’s side effects were possibly linked to the treatment, the study found.

While the main goal of the trial was to examine the safety of the procedure, the decrease in scar tissue in those treated merits a larger study that focuses on broader clinical outcomes, researchers said.

“If we can regenerate the whole heart, then the patient would be completely normal,” Marban said. “We haven’t fulfilled that yet, but we’ve gotten rid of half of the injury, and that’s a good start.”

While the study resulted in patients having an increase in muscle mass and shrinkage of scar size, the amount of blood flowing out of the heart, or the ejection fraction, wasn’t different between the control group and stem cell-therapy group. The measurement is important because poor blood flow deprives the body of oxygen and nutrients it needs to function properly, Srivastava said.

“The patients don’t have a functional benefit in this study,” Srivastava said.