Chronic heavy alcohol use profoundly affects the cardiovascular system, contributing to several life-threatening cardiovascular diseases. Heart rate variability (HRV), or the fluctuations in heart rate, reflects dynamic autonomic nervous system processes that change to meet biological demands and environmental challenges. In the current study, we examined whether HRV metrics are altered in alcohol use disorder (AUD) during waking and sleeping with passive biomonitoring as participants went about their daily lives. Social drinkers (standard deviation: n = 10, 5 female) and treatment-seeking individuals with moderate to severe AUD (n = 16, 7 female) provided continuous, real-world heart rate monitoring for 5 days of monitoring on average (M = 5.27 +/- 2.22). Five indices of respiration and HRV-respiratory sinus arrhythmia (RSA) amplitude, high frequency (HF), low frequency (LF), HF/LF ratio, root-mean-square standard deviation (RMSSD), and standard deviation of the N-N intervals (SDNN)-were analyzed separately for waking and sleeping hours. Both RMSSD and SDNN decreased the longer the participants were awake (Ps < .013). During sleeping hours, HF, RSA amplitude, RMSSD, and SDNN were significantly higher in light social drinkers as compared to patients with AUD (all Ps < .009), indicating higher parasympathetic activation during sleep in the SD versus AUD group. Sleep and waking HRV measures were significantly correlated with patient-reported symptoms of depression and sleep difficulties in the AUD group (Ps < .05). This natural observational study utilizing continuous autonomic biomonitoring in the real world indicates parasympathetic dysfunction that is clearly detectable during sleep in AUD and HRV measures, which are also related to clinical, patient-related symptoms of AUD.