Parthenogenesis is a form of asexual reproduction that occurs naturally in plants, insects, fish, amphibians and reptiles. During this process, unfertilized eggs begin to develop as if they've been fertilized. In 2007, researchers induced human egg cells with chemicals mimicking fertilization so they would undergo the process. The result were parthenogenetic cells that share the same properties as embryos, except that they can't grow further. The cells are akin to pluripotent stem cells derived from embryos, which means they have the ability to develop into different types of cells - including heart cells.
[Researchers] used this knowledge to turn body cells of mice into parthenogenetic stem cells, which were then grown into mature, functional cardiomyocytes. Researchers used these cells to engineer myocardium - heart muscle - with the same structure and function of normal myocardium. The muscle was then grafted onto the hearts of the mice that had contributed the original eggs for parthenogenesis, where it worked the same way as existing muscle.