More than 20 years ago, University of Miami heart transplant cardiologist Joshua Hare became convinced that stem cells infused into heart attack patients would turn into new, healthy cells to replace damaged ones. So far, that hasn’t happened. But Hare, founding director of the university’s Interdisciplinary Stem Cell Institute, still believes that stem cells represent a future in which cardiac care involves less medication and fewer surgeries.

While stem cells haven’t triggered the growth of new cells, patients have seen their conditions improve. The institute has worked with more than 600 patients over the past 20 years, with a more than 60% reduction in patients suffering multiple adverse cardiac events including death, re-hospitalization or progression of heart failure, Hare says.

Why this is happening is “a very complicated scientific question,” Hare says. He believes the cells do stimulate the heart, which then grows its own new cells rather than seeing stem cells replace damaged ones. In addition, the infused pluripotent stem cells seem to eat away at scar tissue after a heart attack.

“By using stem cells, we might be able to not only repair the damaged heart tissue but also prevent the heart from deteriorating further, which is a common consequence of a severe heart attack,” says physician Diana Clavellina, a postdoctoral researcher with the UM stem cell institute. She and Hare published a review paper last August in the journal Expert Opinion on Biological Therapy.

Because the cells haven’t directly created new heart cells, the idea remains controversial, Hare says, with some people advocating that the idea be dropped. But Hare has four human trials underway that are funded by the National Institutes of Health and the Department of Defense.

The running joke in cardiac research is that stem cell infusion therapy for heart attack patients is just five years away. People have been saying it for 20 years. “It hasn’t been an easy road,” he admits. But Hare remains confident that day will come. It might require a different cell formulation or a different dose.

“A lot of treatments in cardiovascular are mechanical — either stents or devices that can be implanted or machines,” Hare says, “And that’s fantastic. I use that clinically. But I really wanted to attack this from a biological standpoint.” He likens stem cell use in heart attack patients to CAR T-cell treatment, which takes a patient’s immune cells and reprograms them to attack cancer cells.

There’s a revolution in medicine, he says. Part of the process is finding things that work, even if you’re not sure why they do.

“The power of science is what allows us to develop new treatments and treat diseases,” he says.