Washington, Nov 18 (IANS) Transplanting a potent form of adult stem cells into the heart muscle of subjects with severe angina lessens pain and improves walking ability.

These findings are the result of the largest national stem cell study for heart disease. The transplant subjects also experienced fewer deaths than those who didn't receive stem cells.

Out of the estimated million people in the US who suffer from chronic, severe angina -- chest pain due to blocked arteries -- about 300,000 cannot be helped by traditional medical treatment namely angioplasty, bypass surgery or stents.

In the 12-month Phase II, double-blind trial, subjects' own purified stem cells, called CD34+ cells, were injected into their hearts in an effort to spur the growth of small blood vessels that make up the microcirculation of the heart muscle.

Researchers believe the loss of these blood vessels contributes to the pain of chronic, severe angina.

'This is the first study to show significant benefit in pain reduction and improved exercise capacity in this population with very advanced heart disease,' said study investigator Douglas Losordo, cardiologist at the Northwestern University Feinberg School of Medicine.

Losordo, also director of the Feinberg Cardiovascular Research Institute, said this study provides the first evidence that a person's own stem cells can be used as a treatment for their heart disease.

He cautioned, however, that the findings of the 25-site trial with 167 subjects, require verification in a larger, Phase III study, said a Northwestern release.

He presented his findings on Tuesday at the American Heart Association Scientific Sessions 2009.