MCU and cardiac rhythm disease: The main possible mechanism for the cardioprotective effects observed on CIR-induced arrhythmias and LET with RuR in this study is its specific inhibition of MCU, decreasing influx of Ca2 into the mitochondrial matrix and Ca2 overload, preserving ATP production and functional integrity of the mitochondria, likely mechanisms for cardiac arrhythmias caused by CIR27.