Japanese researchers have transplanted human induced pluripotent stem cells (iPSCs) in a primate model of myocardial infarction and were able to restore heart muscle and function in monkeys. Developed by Tokyo-based Heartseed Inc., the grafted iPSCs consist of clusters of purified heart muscle cells (cardiomyocyte spheroids) that are injected into the myocardial layer of the heart. Published in Circulation on April 26, 2024, the study showed that the cardiomyocyte spheroids survived long term and showed improved contractile function with low occurrence of post-transplant arrhythmias.