Objective: To unveil the impact of the night shift work routine on the nonlinear dynamics and complexity of cardiac autonomic control in nursing professionals. Methods: This is a cross-sectional observational study, involving 50 nursing (43±8 years), of both sexes, working in a hospital. Participants were allocated into two groups: Day Shift Routine (DSR) (n=25) and Night Shift Routine (NSR) (n=25). Heart rate variability (HRV) was assessed in a laboratory environment by recording the RR intervals (RR) from the electrocardiogram for 10 minutes in the supine position. For HRV analysis, a time series of 256 points was selected to obtain linear and nonlinear indices. Linear indices were calculated in the time domain (mean and variance of RR) and frequency domain (high (HF) and low frequency (LF)), both in absolute and normalized units. For the nonlinear analysis, complexity indices (CI), normalized complexity index, and Shannon entropy were calculated. Symbolic analysis was performed, providing the indices 0V, 1V, 2LV, and 2UV. The indices HF, 2LV, and 2UV represent parasympathetic modulation, while LF and 0V represent sympathetic modulation. An unpaired t-test was conducted, and a significance level of p<0.05 was adopted. Results: The sample consisted of 98% female participants, 6% smokers, a body mass index of 29.95±4.44 kg/m², and an abdominal circumference of 93.02±13.48 CM. Only the CI was significantly higher in the DRS (0.56±0.16) than in the NSR (0.45±0.03) (p<0.001). There was no difference between the groups for the other indices of HRV. Conclusion: Night work in nursing professionals may affect heart beat regularity and predictability, as indicated by a reduced CI. This could suggest compromised cardiovascular adaptability, potentially impacting long-term cardiovascular health, even when traditional heart rate variability measures remain unchanged. Funding: FACEPE – APQ-0578-4.08/22