Core Viewpoint - The article discusses a groundbreaking study published in Nature, where researchers successfully cultivated a small human heart within a pig embryo, which was able to beat and survive for 21 days [1][4]. Group 1: Research Background - Scientists have previously succeeded in transplanting gene-edited pig organs (kidneys, hearts) into humans, and are now exploring the creation of human-animal chimeras to address global organ transplant shortages [3]. - A method to create chimeric animals involves generating embryos lacking specific genes necessary for certain organs and injecting human stem cells into these embryos [4][6]. Group 2: Research Findings - The research team, led by researcher Lai Liangxue, reported the first instance of cultivating a humanized heart in pig embryos, which began beating during the 21-day survival period [4][6]. - The team enhanced the survival of human stem cells in pigs by reprogramming them with genes that prevent cell death and promote growth, and then created pig embryos with two key heart development genes knocked out [7]. Group 3: Observations and Implications - The chimeric pig embryos grew for a maximum of 21 days, after which they could not survive, potentially due to human cells disrupting pig heart function [8]. - The hearts developed to a size comparable to that of a human heart at 21 days and were observed to be beating, although the proportion of human cells in the heart was not disclosed [8][10]. - For future development of transplantable hearts for humans, it is crucial that the organ is composed entirely of human cells to prevent immune rejection [10].