PURPOSE: Sleep deprivation, which is a strong stressor, can greatly affect the cardiovascular system of rescue workers. This study aimed to investigate the effect of 24-h sleep deprivation on heart rate variability (HRV) in young healthy people and the protective effect of metoprolol on arrhythmia. METHODS: Sixty young, healthy subjects (6 women and 54 men), aged 25 +/- 4.5 years, were enrolled in this study. All participants received 24-h continuous ambulatory electrocardiogram monitoring. Arrhythmia, time, and frequency domain parameters were analyzed in subjects at the following three stages: normal sleep stage, sleep deprivation stage, and metoprolol treatment before sleep deprivation stage. RESULTS: After 24-h sleep deprivation, the high frequency (HF) of HRV was significantly decreased (p < 0.05), low frequency (LF) was remarkably increased (p < 0.05), and LF/HF was significantly increased compared with those in normal sleep (p < 0.05). Some subjects presented with mild palpitation due to premature atrial complexes and premature ventricular complexes. At the metoprolol treatment stage, compared with the sleep deprivation stage, LF and LF/HF were significantly reduced, HF of HRV was elevated (p < 0.05), and the total amount of premature atrial and ventricular complexes was decreased. CONCLUSION: The underlying mechanism of arrhythmia and HRV alteration after 24-h sleep deprivation could be attributable to lower vagal activity and elevated sympathetic activity. Metoprolol improves the change in autonomic nervous system activity after 24-h sleep deprivation, which may be responsible for its protective role on arrhythmia in healthy subjects undergoing sleep deprivation.