How do you mend broken hearts?/Scientific American

We are powerless to repair a diseased heart, it is one of the main causes of death in the developed world. A new study done on zebra fish may bring about a revolution in the field of cardiology

By: Charles Choi, Scientific American 
 
The human heart does contain stem cells, but it cannot regenerate itself after an injury and it replaces the damaged muscles with scar tissue. Our inability to repair a diseased heart is the leading cause of death in the developed world.

Cardiologist Mark T. Keating of Harvard Medical School and his research partners achieved the desired goal in May 2005 and were able to induce muscle cells from an adult mammal to divide. This is the first step on the road to medical heart repair. In 2002, Keating found that zebrafish could regenerate without scarring up to a fifth of their hearts within two months after 20% of the muscle tissue of the lower ventricle was removed.

Following this he tried to achieve a similar result in humans. The researchers in his laboratory discovered that the p38 MAP kinase enzyme activity is lowest in mouse embryos when their heart is still growing, and highest when heart muscle cell growth slows down or stops. This suggests that this enzyme is responsible for stopping cell division.
When the researchers used a combination of a drug that inhibits the p38 enzyme with the growth factor FGF1, the combination caused adult rat heart muscle cells to proliferate. Keating and his team believe that a drug-based approach to cardiac rehabilitation is a more elegant approach than stem cell-based approaches. They are now testing mixtures of a p38 inhibitor and a growth factor in animals that have suffered heart attacks to see if they can help the body's most important muscle to heal. Such drugs will revolutionize the field of cardiology.