Figure 1: Two methods of making cardiac tissues. Decellularized hearts are seeded with cardiac cells (a). The seeded cells embed themselves in the matrix framework of the decellularized organ and reestablish cardiac tissue. Alternatively, bottom-up technologies are used to connect small pieces of tissues produced in vitro to reconstruct cardiac tissue artificially. The small pieces used for reconstruction could be regenerated tissues produced from scaffolds, hydrogels, cell sheets, or a combination of such materials. Shown here is an example of cardiac stem cells seeded on hydrogels (b) and cell sheets lifting off of a temperature responsive culture dish (c).