The trial involved 22 patients with progressive heart failure or an enlarged heart and whose current medication was no longer effective. They received either an injection of the stem cell treatment into their heart muscle or a placebo.
The participants were monitored for a year and the clinicians reported no serious side effects among those who received the stem cells compared to the control group.
The patients who received the stem cell injections displayed fewer major heart-related problems and observed improvements in their ability to walk without becoming breathless. These patients were also more likely to show improvements in ejection fraction, which measures how much blood the heart pumps out with each beat.
Dr Timothy Henry, director of research at the Minneapolis Heart Institute, who led the study, said: 'A number of people with heart failure have slowly progressing disease despite medication and/or device therapy. If we could have a therapy for this group that would slow the progression of heart failure, it would be economic and change the disease process tremendously'.
The treatment involves growing a patient's own bone marrow cells in culture for 12 days. This increases the number of immune cells and stem cells called mesenchymal stem cells, which can differentiate into several cell types including heart cells. This enriched cell population is injected directly into the heart muscle. Using a patient's own cells minimises the risk of rejection.
'This study tells us that injecting stem cells into the heart muscle of a patient with chronic heart failure may be beneficial', says Dr Sandeep Jauhar, of the Long Island Jewish Medical Center, New York, who was not involved in the study.
He added that despite available treatments being effective, they are reaching a plateau. 'We do need a new way of treating heart failure if we want more improvement', said Dr Jauhar, who continued to say that it is too early to say whether this new stem cell therapy could fill that role.
'It shows some improvement in pumping parameters of the heart, but that doesn't mean you will live longer', he said.
Although these results are preliminary, the researchers say it provides enough evidence for a larger clinical trial with more participants.