Bone marrow stem-cell therapy is a safe treatment for people who have suffered a severe heart attack, a small new study suggests.

By using stem cells found in the bone marrow, scientists are a step closer to developing a therapy that could help repair damaged heart cells, said study researcher Dr. Jay H. Traverse, a cardiologist at the Minneapolis Heart Institute in Minneapolis.

Stem cells make growth factors that help other cells survive, and they may be able to improve blood flow to the damaged areas in the heart, Traverse said. The cells in the study, called bone marrow-derived mononuclear cells, have been studied for their benefits in regenerating damaged cells.

Researchers randomly assigned 40 patients who had suffered a severe heart attack to receive either the stem-cell treatment or a placebo treatment. They were given these treatments three to 10 days after their arteries had been successfully unblocked and opened with stents.

No one in the stem cell group had a major adverse reaction, and all the patients are still alive today, according to the study.

As with any Phase 1 study, the goal was to establish the safety of the treatment, not to test its efficacy or superiority over other treatments, Traverse said.

But in the study, the stem cell therapy did have a positive effect in keeping the size of patients' hearts small, he said.

"Over time, after you have a heart attack, the heart tends to enlarge and it leads to congestive heart failure," Traverse said. But because the hearts of those who received the stem cells did not become enlarged like those of the the placebo group, it appears that treatment with stem cells did at least have a positive effect.

The study was published in the September issue of the American Heart Journal.