The view that ROS are either harmful or beneficial is very simplistic.
ROS can mediate specific post-translational modifications of biomolecules involved in intracellular signaling networks.
Redox signaling involves spatially and temporally confined ROS production which modulates activity of signaling molecules.
The NADPH oxidase proteins Nox2 and Nox4 are major enzymatic sources of ROS involved in cell signaling in cardiomyocytes.
Redox signaling in the heart is involved in acute and chronic cardiac adaptations to diverse stresses.