The present study demonstrates that intraperitoneal injection of H2 protects against ISO-induced cardiac hypertrophy and dysfunction in vivo and H2-rich medium attenuates ISO-mediated cardiomyocyte hypertrophy in vitro. The cardioprotection of H2 is mediated by direct interruption of NADPH oxidase expression and alleviating mitochondrial damage, these lead to inhibit the accumulation of ROS, and subsequently block downstream ERK1/2, p38, and JNK signaling. Here, FMO5 is linked to cardiac hypertrophy.