Introduction Germ cells are the only cells that link the generations, and their unique capacity to transmit information from parent to offspring has interested scientists for many years. A striking feature of germline stem cells, very much like any other stem cells, is their ability to self-renew while remaining capable of generating numerous differentiated daughter cells. Recent research with spermatogonial stem cells (SSCs), male germline stem cells, in the adult mouse demonstrates the potential of these stem cells in clinical application for the treatment of infertility and regeneration of damaged organs.1-6 Potential applications of human SSCs for the treatment of infertility and germline gene therapy have been discussed in reviews.6,7 Here we discuss the origin and properties of male germline stem cells, and their implications for basic research and for therapeutic cardiac regeneration.