July 3 (UPI) -- Heart function in monkeys has been restored with human stem cells, according to a study, showing promise the method will work in humans with heart failure.

Researchers at the University of Washington School of Medicine in Seattle found the hearts pumped vigorously again after embryonic stem cells formed new muscle in the organ. Their findings were published Monday in the journal Nature Biotechnology.


In some cases, heart function was restored to better than 90 percent of normal.

"Our findings show that human embryonic stem cell-derived cardiomyocytes can re-muscularize infarcts in macaque monkey hearts and, in doing so, reduce scar size and restore a significant amount of heart function," Dr. Charles "Chuck" Murry, professor of pathology at the UW School of Medicine, said in a press release. "This should give hope to people with heart disease."

About 610,000 people die of heart disease in the United States every year, making it the leading cause of death for men and women, according to the Centers for Disease Control and Prevention.

Damaged heart muscles are replaced with scar tissue. As the heart grows weaker, not enough blood can supply the body with oxygen.

A heart's lost muscle function hadn't previously been restored in humans. Macaque monkeys, which have similar heart size and physiology to humans, were used in the study.

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After heart attacks, the left ventricular ejection fractions went from about 65 percent to 40 percent among the primates, according to the researchers.

After two weeks, heart cells grown from human embryonic stem cells -- roughly 750 million -- were injected into and around the young scar tissue. A control group received a cell-free version of the solution used to inject the stem cells for the other monkeys.

Four weeks after the stem cell injections, the ejection fraction of the control animals remained essentially unchanged at about 40 percent. In the treated animals, however, it rose to 49.7 percent, which is about halfway back to normal.

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MRI scans confirmed new heart muscle had grown within what had been scar tissue in the treated hearts compared with none in the control group.

Over three months, treated animals continued to improve, up to 66 percent, as the untreated ones declined, and new muscle tissue had replaced 10 percent to 29 percent of the scar tissue.

The researchers plan human clinical trials in 2020, and ultimately developing a treatment for people shortly after heart attacks in an effort to prevent heart failure.

Murray, who has studied using stem cells for heart disease for about 20 years, said the procedure would be similar to a coronary angiogram.

"What we hope to do is create a 'one-and-done' treatment with frozen 'off-the-shelf' cells that, like O-negative blood, can go into any recipient with only moderate immune suppression," Murry said.