A study published in *Nature* (2014) demonstrates that human embryonic stem cell-derived cardiomyocytes (hESC-CMs) can regenerate non-human primate hearts. The research shows that hESC-CMs can be produced at a clinical scale (>1 billion cells/batch) and cryopreserved with good viability. In a non-human primate model of myocardial ischemia-reperfusion, cryopreserved hESC-CMs were delivered into the infarcted heart, resulting in significant remuscularization. The hESC-CMs showed progressive maturation over three months, with electromechanical coupling to the host heart, as evidenced by synchronized calcium transients with the host electrocardiogram. However, arrhythmias were observed in primates, suggesting potential risks for clinical translation. The study highlights the feasibility of large-scale hESC-CM production and delivery, with implications for future human heart failure therapies. The research also addresses challenges in scaling up production and ensuring safety, emphasizing the need for further studies to mitigate arrhythmic complications. The findings suggest that hESC-CMs could be used to regenerate human hearts, but careful consideration of safety is required. The study provides important insights into the potential of stem cell-based therapies for heart regeneration.A study published in *Nature* (2014) demonstrates that human embryonic stem cell-derived cardiomyocytes (hESC-CMs) can regenerate non-human primate hearts. The research shows that hESC-CMs can be produced at a clinical scale (>1 billion cells/batch) and cryopreserved with good viability. In a non-human primate model of myocardial ischemia-reperfusion, cryopreserved hESC-CMs were delivered into the infarcted heart, resulting in significant remuscularization. The hESC-CMs showed progressive maturation over three months, with electromechanical coupling to the host heart, as evidenced by synchronized calcium transients with the host electrocardiogram. However, arrhythmias were observed in primates, suggesting potential risks for clinical translation. The study highlights the feasibility of large-scale hESC-CM production and delivery, with implications for future human heart failure therapies. The research also addresses challenges in scaling up production and ensuring safety, emphasizing the need for further studies to mitigate arrhythmic complications. The findings suggest that hESC-CMs could be used to regenerate human hearts, but careful consideration of safety is required. The study provides important insights into the potential of stem cell-based therapies for heart regeneration.