Cardiovascular diseases (CVDs) are a leading cause of death globally. Excessive production of reactive oxygen species (ROS) is detrimental to cardiomyocytes (CMs), triggering inflammation, inducing cell death, disrupting calcium homeostasis, and leading to arrhythmia. Thus, ROS is considered a common pathological factor in CVDs. Although the efficacy of antioxidants targeting ROS is currently limited, nanotechnology offers opportunities to develop antioxidants with improved selectivity and bioavailability, which can effectively prevent or treat oxidative stress-related CVDs. Cerium oxide nanozymes (CeONZs) can efficiently scavenge excessive ROS by mimicking the activity of endogenous antioxidant enzymes. However, their nanosafety and efficacy in human CMs remain unclear, posing a critical issue to be addressed before clinical applications. Due to the scarcity of primary human CMs, human pluripotent stem cells (hPSCs) and their derived cardiomyocytes (hPSC-CMs) provide a valuable source for modeling CVDs and their therapeutic interventions. This chapter presents a preparation method for CeONZs and outlines the assessment of their biosafety and antioxidant efficacy in hPSC-CMs.