Abstract: AIM:To examine the expression of Tbx18 and Wt1 in embryonic hearts and to explore whether Tbx18 and Wt1 are expressed in the myocardium. METHODS: Mouse embryonic hearts were collected at different stages for immunofluorescence co-staining with either Tbx18 and the cardiac transcription factor Nkx2.5 or Wilms tumor 1 (Wt1) and Nkx2.5. RESULTS: Tbx18 and Wt1, but not Nkx2.5, were expressed in the proepicardium and epicardium. Tbx18 was expressed in cells within the heart from E10.5 to at least E14.5. These Tbx18-expressing cells were Nkx2.5 positive, except for a few cells that were Nkx2.5 negative at E14.5. Wt1 was expressed in cells within the heart from E12.5 to at least E14.5, but these Wt1-expressing cells were Nkx2.5 negative. CONCLUSION: The results of this study demonstrate that Tbx18 is expressed in the myocardium from E10.5 to at least E14.5 and Wt1 is expressed within the heart from E12.5 to at least E14.5, but not in the myocardium. These findings may provide some new insights on the role of epicardial cells in cardiac regeneration.