Congenital heart disease occurs in 1% of liveborn infants, making it the most common birth defect worldwide. Many of these children develop heart failure. In addition, both genetic and acquired forms of dilated cardiomyopathy are a significant source of heart failure in the pediatric population. Heart failure occurs when the myocardium is unable to meet the body's metabolic demands. Unlike some organs, the heart has limited, if any, capacity for repair after injury. Heart transplantation remains the ultimate approach to treating heart failure, but this is costly and excludes patients who are poor candidates for transplantation given their comorbidities, or for whom a donor organ is unavailable. Stem cell therapy represents the first realistic strategy for reversing the effects of what has until now been considered terminal heart damage. We will discuss potential sources of cardiac-specific stem cells, including mesenchymal, resident cardiac, embryonic, and induced pluripotent stem cells. We will consider efforts to enhance cardiac stem cell engraftment and survival in damaged myocardium, the incorporation of cardiac stem cells into tissue patches, and techniques for creating bioartificial myocardial tissue as well as whole organs. Finally, we will review progress being made in assessing functional improvement in animals and humans after cellular transplant.