Abstract: Reactive oxygen species (ROS) are a class of oxygen-containing free radicals or non radical molecules, which are so highly reactive that they can react with proteins, lipids and DNA in organisms. ROS play pivotal roles in the heart under both physiological and pathophysiological conditions, so understanding the production process of reactive oxygen species in cardiac cells is important to cardiac research. This review summarizes main ROS production pathways in cardiomyocytes.