Abstract--The present study examined whether nestin⁺ neural-like stem cells detected in the scar tissue of rats 1 week after myocardial infarction (MI) were derived from bone marrow and/or were resident cells of the normal myocardium. Irradiated male Wistar rats transplanted with -actin promoter-driven, green fluorescent protein (GFP)-labeled, unfractionated bone marrow cells were subjected to coronary artery ligation. Three weeks after MI, GFP-labeled bone marrow cells were detected in the infarct region, and a modest number were associated with nestin immunoreactivity. The paucity of GFP⁺/nestin⁺ cells in the scar tissue provided the impetus to explore whether neural-like stem cells were derived from cardiac tissue. Nestin mRNA and immunoreactivity were detected in normal rat myocardium, and transcript levels were increased in the damaged heart after MI. In primary-passage, cardiac tissue-derived neural cells, filamentous nestin staining was associated with a diffuse, cytoplasmic glial fibrillary acidic protein signal. Unexpectedly, in viable myocardium, numerous nestin⁺/glial fibrillary acidic protein⁺ fiberlike structures of varying length were detected and observed in close proximity to neurofilament-M⁺ fibers. The infarct region was likewise innervated, and the preponderance of neurofilament-M⁺ fibers appeared to be physically associated with nestin⁺ fiberlike structures. These data highlight the novel observation that the normal rat heart contained resident nestin⁺/glial fibrillary acidic protein⁺ neural-like stem cells, fiberlike structures, and nestin mRNA levels that were increased in response to myocardial ischemia. Cardiac tissue-derived neural stem cell migration to the infarct region and concomitant nestin⁺ fiberlike innervation represent obligatory events of reparative fibrosis in the damaged rat myocardium.