A clinical trial to test the safety of treating heart attack damage with stem cells (search) is about to get under way, following a study that showed the therapy helped in pigs.

Two patients have been enrolled so far at Johns Hopkins Hospital in Baltimore, and a total of 48 are expected to take part across the country, said Dr. Joshua M. Hare, who is leading the study.

"Anytime something new comes along there is a sense of excitement and that's the feeling that we have. And we obviously hope it will be borne out by the results," Hare said in a telephone interview.

The process uses adult stem cells taken from the bone marrow. These cells, called mesenchymal cells, have been shown to give rise to a variety of cell types. While they don't have the potential to develop into as many cell types as embryonic stem cells, using them avoids the controversy over taking cells from a human embryo.

In tests in pigs, stem cells taken from another pig's bone marrow were injected into the animal's damaged heart. After just two months, the stem cells had helped restore heart function and repaired damaged heart muscle by 50 percent to 75 percent.

Those results are reported in Tuesday's issue of Proceedings of the National Academy of Sciences.

The work is an early indication that stem cells may have therapeutic value in treating heart attacks, but a lot of work remains to be done, said Dr. Sidney Smith, cardiology chief at the University of North Carolina at Chapel Hill.

It is a long way between successful work in a few pigs and a therapy that could benefit thousands of humans, said Smith, a spokesman for the American Heart Association. In the meantime, he said, efforts such as stopping smoking and controlling cholesterol can help prevent many of those heart attacks.

The planned tests in humans are a Phase I trial, meaning that the goal is merely to make sure the procedure is safe in humans. Only after safety is established will the scientists move on to a Phase II trial to see if it works as well in people as in pigs.

But researchers will be checking to see if the procedure is helping the people. Hare said study participants will be watched for two years. At six months after the treatment they will undergo an MRI scan to check their heart function.

Hare said he hopes that will be taking place by mid-2006.

In the initial trial, he said, the cells will be infused into the blood stream. In the Phase II trials, a variety of methods would be used to deliver the cells, he said.

In the pig study, the researchers studied 14 animals that had had heart attacks. Seven were given the stem-cell therapy and seven were not. The adult stem cells were directly injected into the heart muscle through a catheter.

The seven treated pigs had their heart muscle contraction restored to levels that existed before the heart attacks and dead scar tissue nearly disappeared after therapy, the researchers said.

In the seven other pigs, which were injected with an inert placebo, no recovery was observed and the animals' condition worsened, leading to the development of congestive heart failure within two months after heart attack, according to the researchers.

The research was funded by the Johns Hopkins University School of Medicine, Osiris Therapeutics, The Donald W. Reynolds Foundation and the National Institutes of Health.