Cardiac regeneration is a broad effort that aims to repair irreversibly damaged heart tissue with cutting-edge science, including stem cell and cell-free therapy. Reparative tools have been engineered to restore damaged heart tissue and function using the body's natural ability to regenerate. The heart is unable to regenerate heart muscle after a heart attack and lost cardiac muscle is replaced by scar tissue. Researchers are using stem cells in two important ways to improve cardiac health. Heart stem or progenitor cells are multipotent cells residing in the adult mammalian heart that are capable of self-renewing and generating coronary vessels. The difficulty in regenerating damaged myocardial tissue has led researchers to explore the application of embryonic and adult-derived stem cells. The Harvard Stem Cell Institute is developing new techniques to grow cardiac muscles. The researchers used 3-D human heart tissue grown in the lab from human stem cells to test the cell combination.