An adult zebra fish can regenerate a damaged heart with no scar formation. This remarkable phenomenon has been seen in other fish and amphibians as well, but never before in a mammal.

Now researchers from the University of Texas Southwestern Medical Center report in the current issue of Science that the mammalian newborn heart can fully heal itself.

Dr. Hesham Sadek, a cardiologist at the medical center, and his colleagues worked with mice and found that if a portion of the heart was removed within the first week of life, the heart grew back completely.

The researchers removed about 15 percent of the lowest portion of the heart, known as the apex, in laboratory mice. Within three weeks, the lost tissue regenerated itself and the hearts were healed.