An electromagnetic field is applied to transplanted cells during their transplantation culturing to achieve confluence and alignment of transplanted cells into damaged tissue and organs, therefore improving the synchronization of electrical and mechanical tissue or organ functions. The electromagnetic field may be applied by catheter based devices to a selected portion of tissue or to the entire surface of a hollow body cavity or organ, such as a heart chamber. The electromagnetic field is provided by an expansible net or array from a catheter or on an inflatable balloon or stent. The electromagnetic field is also provided by an implantable net or array of electrodes which may either be hardwired to a pulse generator or coupled by means of wireless or inductive transmission.