Provided are a cell sheet and a three-dimensional structure thereof that include at least mesenchymal stem cells and myoblasts isolated from a cell culture support and that are to be applied to heart disease. Use of the cell sheet and the three-dimensional structure thereof including mesenchymal stem cells and myoblasts can notably improve cardiac functions compared with a conventional technology, i.e., use of cell sheets composed of myoblasts only or mesenchymal stem cells only. Furthermore, the cell sheet itself has high strength, and the transplantation procedure is also improved.
