Boston, MA—Once a mere fantasy, the idea of growing new, healthy heart tissue to replace damaged or diseased heart muscle is inching closer to reality. Researchers are exploring several routes to grow new heart muscle, according to the January issue of the Harvard Heart Letter .

One approach uses adult stem cells found in bone marrow or the bloodstream. Injected or infused into damaged heart tissue, these stem cells can take up residence and grow into healthy heart muscle. An alternative is to use immature muscle cells taken from the thigh; when injected into the heart, they adopt the characteristics of heart cells.

Scientists are also pursuing the possibility of using growth factors, hormones, or other substances to stimulate dormant stem cells in the heart itself to multiply and grow into healthy heart tissue. And a particularly innovative self-repair strategy involves coaxing some heart cells to regress to a stem-cell–like state and then stimulating them to produce young, healthy heart cells.

The Harvard Heart Letter points out that while the field of cardiac repair is in its infancy, the long-term implications for heart disease are great, particularly for people with heart failure, a condition in which the heart is so damaged that it becomes difficult for it to deliver enough blood to meet the body's demands. Although current therapies can ease symptoms of heart failure and lengthen life expectancy, they don't reverse the damage. Stem cell research may also someday enable doctors to create replacement heart valves tailored to a patient's own body or to grow new blood vessels around blocked coronary arteries.

Long-term tests are needed to determine the safety and effectiveness of these strategies, says the Harvard Heart Letter. And heart disease certainly isn't the only condition that might benefit from these techniques, which are also being tested for treating diabetes, Parkinson's disease, spinal cord injuries, Alzheimer's disease, and other problems.