I'm not sure exactly which zebrafish they're talking about, but this picture is a pretty one of "zebrafish". Photo by Saspotato
Zebrafish have the ability to grow back missing parts of their hearts, or at least that’s what a new study in the March 25 issue of Nature implies. “…researchers working at the Salk Institute for Biological Studies and the Center of Regenerative Medicine in Barcelona (CMRB) identified a fish heart cell population that is the source of this astonishing healing feat, a finding that could provide insight into how mammalian hearts might be coaxed into repairing themselves after injury brought on by heart attack.”
Source: Underwater Times
Girella zebra is the species :)