Diagnostic value of low heart rate variability by time domain and association with autonomic nervous system autonomic nervous system frequency spectrum Time domain Low HRV parasympathetic HF rMSSD rMSSD < 15 ms pNN50 pNN50 < 0, 75% Sympathetic, parasympathetic LF SDNN index (or ASDNN) ASDNN < 30 ms Sympathetic, parasympathetic VLF SDNN index (or ASDNN) ASDNN < 30 ms Sympathetic, parasympathetic ULF SDNN SDNN < 50 ms SDANN SDANN < 40 ms The indicators of heart rate variation according to the frequency spectrum (ms2) - VLF: - LF: - HF: - LF / HF: Criteria for low HRV analyzed by frequency spectrum were not found.