Cardiomyocyte proliferation refers to the ability of cardiac muscle cells to progress through the cell cycle and continue to divide. Traditionally, cardiomyocytes were believed to have little to no ability to proliferate and regenerate after birth.[1] Although other types of cells, such as gastrointestinal epithelial cells, can proliferate and differentiate throughout life,[2] cardiac tissue contains little intrinsic ability to proliferate, as adult human cells arrest in the cell cycle.[3] However, a recent paradigm shift has occurred. Recent research has demonstrated that human cardiomyocytes do proliferate to a small extent for the first two decades of life.[4] Also, cardiomyocyte proliferation and regeneration has been demonstrated to occur in various neonatal mammals in response to injury in the first week of life.[5][6] Current research aims to further understand the biological mechanism underlying cardiomyocyte proliferation in hopes to turn this capability back on in adults in order to combat heart disease.