Researchers from Tokyo Medical and Dental University (TMDU) use mouse embryonic stem cells to engineer three-dimensional functional heart organoids resembling the developing heart.Heart development as it happens in vivo, or in a living organism, is a complex process that has traditionally been difficult to mimic in vitro, or in the laboratory. In a new study, researchers from Tokyo Medical and Dental University (TMDU) developed three-dimensional functional heart organoids from mouse embryonic stem cells that closely resemble the developing heart.