Background: The high incidence and risk of cardiovascular disease have motivated the development of new therapeutic strategies such as biological substitues that restore, improve tissue function to help treat associated pathologies. Therefore, we have developed a viable cell-patch, rat mesenchymal stem cell (MSC) in scaffold-based polymer. We report our investigations and experiences of the in vivo survival of this bioengineered rat mesenchamal stem cells in rat heart tissue. Meshods: Primary cultured mesenchymal stem cells (MSCs) derived from rat bone marrow were prelabeled 4',6'-diamino-2-phenyl-indole (DAPI) and seeded into a poly glycolic acid caprolactone lactide (PGCL) patch for 48hours, a biodegradable polymer, to form graft. For ex vivo studies, growth patterns of the cells within the graft were evaluated by SEM and histologic examination; in vivo studies, the graft was cultured for 48 hours and then implanted into epicardial myocardium in normal rat heart (n=4) by simple tagging-suture. After the graft implantation, the rats were harvested at 1, 3, 5, and 7 weeks following surgery and the grafts were evaluated histologically. The survival of the transplanted MSCs were comfirmed by 3-D image analysis. Results: The inoculum cells were attached and grew in scaffold-based patch mesh by SEM. When implanted onto epicardial myocardum, the cells within the graft survived at least 7 weeks with negligible inflammatory cell infilteration. These cells did not show the definite phenotype of cardiomyocyte with cardiac troponin-I and alpha-actinin. Conclusion: Despite of limitation of small number, Rat MSCs can grow in scaffold-based PGCL polymer. The MSCs seeding of PGCL polymer were survived successfully in rat epicardial myocardum