The implantation of the Bone Marrow Mesenchymal Stem Cells (BMSCs) into the heart has been reported to be effective for the treatment of myocardial infarction; however, the methods most suitable for supporting stem cell growth in a myocardial patch, still remain unknown. We used a new polymer material composed of poly(3-hydroxybutyrate-co-3-hydroxybutyrate) [P(3HB-co-3HB)] co-cultured with BMSCs to create a myocardial patch. The BMSCs were obtained from healthy male BSL-C57 mice. The cells were treated with 5-azacytidine to investigate their differentiation into cardiomyocytes. The cells were seeded for 24 hours onto the P(3HB-co-3HB) biological material films (n=8). Cell-biomaterial constructs were fixed and analyzed using different methods. BMSCs were CD34(-), CD45(-), CD90(+) (low) and CD73+. The cells were stained with anti-cardiac troponin T (cTnT) and anti-connexin 43 (CX43) antibodies after 5-azacytidine treatment. Scanning electron microscopy revealed that the morphology of the BMSC was normal and that cell numbers were more abundant on the P(3HB-co-3HB) material surfaces. The growth curve of the BMSCs on the biomaterial patches showed the P(3HB-co-3HB) material enhanced good stem cell growth. Owing to its excellent biocompatibility and biodegradability properties, in particular its porosity, the P(3HB-co-3HB) is hailed as an optimal material to support myocardial cell growth and to create a myocardial patch in patients with myocardial infarction.