Starfish can regenerate their legs, and worms can survive being cut in two, but these feats pale when compared to the common zebra fish, which can fix a broken heart. These common, black and white striped aquarium favorites have nothing to do with soothing jilted lovers, of course. But in addition to being able to regenerate fins and eye parts, zebra fish can regenerate heart tissue.
In an experiment that was certainly no fun for the fish, Harvard scientists surgically removed twenty percent of the heart tissue of ten adult zebra fish, then put them back in the water to see what would happen. At first the fish swam weakly near the bottom of the tank; a microscope revealed that in the early stages of recovery, scar tissue partially clotted the wounded organ.
However, after about ten days the fish were back to their normal routines, swimming vigorously. Of the ten fish with broken hearts, eight fully recovered. Another microscope inspection revealed that the recovered fish had regenerated their heart tissue with virtually no scarring.
How, exactly, zebra fish mend their broken hearts is of great interest to scientists. When people recover from a heart attack their hearts are never quite the same. A healing heart normally accumulates scar tissue instead of muscle growth. The scarred, weakened heart cannot contract and pump blood as efficiently as an undamaged heart.
Since zebra fish and humans share many of the genes responsible for cell regeneration, further study may lead to techniques for scar-free human heart repair.