A research team led by Mark T. Keating showed that zebrafish can regenerate heart muscle within two months after a severe injury. The team, from the Howard Hughes Medical Institute at Children’s Hospital Boston, also identified a possible genetic and molecular model for regeneration in zebrafish that could help direct further research in humans. The findings, while still in an early stage, might someday benefit millions of people who suffer heart attacks or experience other forms of cardiac injury. The zebrafish is the subject of active study because of its ability to regenerate spinal cord, retina, and fins. This finding points to the study of zebrafish heart regeneration as a means to understand and reduce cardiac injury in humans. When a human heart is injured, it cannot “grow back” the damaged muscle, which is instead replaced by scar tissue. Too much scarring can impair the heart’s ability to pump and can lead to life-threatening arrhythmias. Keating and his colleagues believe that zebrafish, unlike humans, have especially vigorous development of new heart-muscle cells, or cardiomyocytes. This proliferation of cells regenerates the heart muscle with little or no scarring. The research was reported in the Dec. 13, 2002 issue of Science.