The biomedical effects of molecular hydrogen have aroused public and academic interest in recent years. Because of its high diffusivity and very small structure, hydrogen has the ability not only to cross the blood brain barrier, but also to infiltrate through the cytomembrane to the cytoplasm, mitochondria, nuclei, endoplasmic reticulum and other subcellular structures, even to interact inner motif of biomacromolecules. It has been proven that hydrogen shows effects on the prevention and treatment of cardiac injury induced by radiation, ischemia-reperfusion, cardiac allografts, cardiopulmonary resuscitation and cardiopulmonary bypass nearly without side effects. These effects have been suggested to be associated with its antioxidant activity, anti-inflammatory effect, anti-apoptosis and role in regulating of mitochondrial metabolism, but further studies are greatly needed for better and deeper understanding of the protective effects of hydrogen in cardiac injury.