Cardiomyocytes deceased during myocardial infarction (MI) are replaced with non-contractile scar tissue, which has a great chance to cause heart failure. Repair of dead or injured myocardium and improvement of cardiac function remain a serious challenge for the therapy of heart failure. Recently, stem cells have been transplanted in experimental settings to replace lost myocardium. This article summarizes the recent experimental findings on transplantation of embryonic stem cells (ESCs) and their derived cells in animals with myocardial injury and highlights the progresses in research of these particular cell types. Beneficial effects of cell transplantation with other cell types in injured hearts have been detailed in other reviews. ESCs are pluripotent cells derived from early mammalian embryos at the blasto-stage. These cells have the capacity for prolonged undifferentiated proliferation or differentiation into all of specialized somatic cell types of the body in culture, including cardiomyocytes. Because of the great ability of proliferation and differentiation to mature tissues, ESCs are a potential valuable resource for cell therapy targeting regeneration of functional myocardium in diseased hearts. In recent animal studies intramyocardial transplantation of ESCs or their differentiated cardiac-like cells regenerated injured myocardium and improved heart function in infarcted animal models. In addition, intravenous infusion of ESCs significantly increased the survival rate and attenuated myocardial injury in viral myocarditic mice. Development and characterization of cardiomyocytes in vitro from human ESCs have been reported recently. However, many ethical, political, and scientific barriers have to be overcome before clinical utilization of human ESCs and their differentiated cells for treating end-stage cardiac diseases.