Plasma irradiation not only produces a variety of reactive species, but can also modify the molecular structure of materials at the atomic level. In recent years, it has been focused on the effects of specific chemical reactions induced by low-temperature plasma irradiation on biological activities, such as sterilization, wound healing, and anti-tumor effects. However, the molecular mechanisms of these effects have remained unclear. We found that irradiation of non-equilibrium atmospheric pressure plasma with humidified helium gas into cysteine (Cys-SH) solution produces sulfur metabolic intermediates such as cysteine persulfide (Cys-SSH) and thiosulfate ion. We previously showed that reactive sulfur species (RSS) such as Cys-SSH play an important role in mitochondrial energy metabolism and that RSS metabolism contributes to ischemic tolerance. Plasma-irradiated cysteine solution (Cys^*) significantly suppressed mitochondrial dysfunction in hypoxic cardiomyocytes and myocardial cell death induced by reoxygenation. The accumulation of sulfide and intracellular RSS catabolism under hypoxia was significantly inhibited by Cys^*. Furthermore, injection of Cys^* into mice improved cardiac function after ischemia/reperfusion injury. These results suggest that Cys^* containing various sulfur intermediates exerts a cardioprotective effect by negatively regulating intracellular RSS catabolism in the absence of O₂ and by maintaining energy metabolism in mitochondria.