Heart attack patients who got infusions of stem cells within a week of a heart attack had fewer episodes of irregular heartbeat and better recovery than those who didn't get the treatment, according to a study reported Sunday by a University of Miami researcher.

It was the first study in humans using a special kind of stem cell that has been shown to seek out damaged or inflamed areas in the body and repair them. The cells are noncontroversial because they are taken from adult bone marrow, not human embryos.

"Over the six-month follow-up period, the stem cell patients had lower rates of side effects such as cardiac arrhythmias, and they had significant improvements in heart, lung, and [overall] function," said Dr. Joshua Hare, professor of medicine and director of the Interdisciplinary Stem Cell Institute at Miami's Miller School of Medicine.

Hare, who presented the results at a meeting of the American College of Cardiology in New Orleans, was the lead investigator for the study, which included 53 heart attack patients recruited at 10 medical centers across the country.

Hare said the trial was designed to assess the safety of the experimental treatment using a particular type of stem cells called mesenchymal cells, derived from adult bone marrow. But he said the early results of the study, financed by a Baltimore company that plans to seek federal approval for the treatment after more study, showed very clearly that the cells were beneficial to the patients.

"We had seen results in animals, but I have to say I was truly surprised [at the human study results] because the study design was to look at safety, and we saw improved heart function, improved lung function and improved [recovery]," Hare said.

The cells were selected because they have been shown to seek out inflammation and repair it, Hare said. Patients who had the most heart damage from their heart attacks improved the most, he said.

The cells can be taken from different donors and don't have to be genetically matched to the recipients. They can be grown quickly in the lab, and once infused intravenously in the patient they home in on injured areas and work to repair them.

Hare cautioned that the results are preliminary and more research must be done. Hare said earlier studies in heart patients using bone marrow stem cells showed promise, but this is the first human trial using just the mesenchymal cells.

The study was paid for by Osiris Therapeutics, of Baltimore, which created the cell treatment as a product called Provacel and hopes to proceed with a second round of studies before seeking approval from the U.S. Food and Drug Administration to bring the treatment to market.

Dr. Jay Traverse, a cardiologist at the Minneapolis Heart Institute, one of the clinical trial sites, said unlike other cell therapies, these cells are readily available and easily administered through a standard IV line.