As cold-water immersion becomes more popular and accessible, it is important to explore potential risks. This study examines the cardiac autonomic response and arrhythmia occurrence in healthy adolescents during face and body immersion. Healthy ninth-grade students, aged 15–16 years, were recruited to perform face immersion (FI) in 10°C water and body immersion in 2°C water (IWI). Electrocardiograms (ECGs) were continuously recorded, and the heart rate (HR) response and occurrence of arrhythmias were assessed. Among the 54 individuals performing FI, six had supraventricular extrasystoles, and two had ventricular bigeminy. Among the 20 performing IWI, four had supraventricular extrasystoles. The HR response was more pronounced during FI compared to IWI (p < 0.001). During both FI and IWI, girls showed initially higher HR and more pronounced HR reduction than boys, but there were no significant sex differences (p = 0.26). During the first 30 seconds of IWI, boys maintained a steady HR (p = 0.176), while girls experienced a near-linear reduction (p = 0.009). This study indicates a low risk of severe arrhythmias when briefly immersing the body in ice-cold water in healthy adolescents. However, the risk could increase if combined with face submersion and apnea.