Heart, stroke and other cardiovascular diseases are responsible for ~17 million deaths per year globally and this number is predicted to reach 23.3 million by 2030. Cardiovascular diseases impose a staggering annual cost of $300 billion on the U.S. health care system. Heart transplantation is the ultimate solution to end-stage heart failure. However, a major limitation in treating cardiac injury is the limited availability of donors; as a result, only a small fraction of patients will benefit from heart transplantation. Tissue engineering holds a great promise to create functional tissue constructs that can reestablish the structure and function of injured tissue with exciting success stories. However, many challenges regarding their development still remain. It is the goal of this project to develop a novel 3D bioprinting technology to fabricate cardiac tissues made from cell-laden hydrogels with engineered microvasculature. By integrating the advanced 3D bioprinting with stem cell technology, functional cardiac tissues will be created with biomimetic 3D microarchitecture and functional vasculature. This novel 3D-printed cardiac tissue will heal the damaged heart and improve its function to pave the way for a superior treatment option for the millions of cardiac patients in the U.S. Heart disease and other cardiovascular diseases are the #1 killer in California and remain a leading cause of disability and death. A major limitation in treating cardiac injury is the failure of current therapies to induce myocardium regeneration. Due to the limited availability of donors, only a fraction of individuals who could benefit from heart transplantations actually receive them. One possible avenue for remedying this situation is to artificially engineer cardiac tissues. Tissue engineering techniques have been successfully applied to engineer many types of tissue; however, many challenges regarding their development still remain. This proposal aims to make an advance in tissue engineering by developing a novel 3D bioprinting technology to fabricate tissues made from cell-laden hydrogels with engineered microvasculature. The completion of this work will be a paradigm shift and a landmark achievement in efforts towards clinical treatments of vascularized cardiac tissue using stem cells. This advanced technology can also have a significant economical impact as heart diseases impose a staggering annual cost of $300 billion on the U.S. health care system. In addition, the development of the 3D bioprinting technology and advanced biomaterials will keep California and the U.S. as a whole in the leading position in this emerging field.