- Background The bipolar affective disorder is long been speculated to have an autonomic involvement. Nonlinear analysis of heart rate variability has recently been shown to be a reliable noninvasive test for quantitative assessment of the central sympathovagal interaction that modulates cardiovascular autonomic function. Methods We studied 32 euthymic bipolar patients and 24 controls. A high-resolution electrocardiogram was obtained during complete rest. Nonlinear analysis (Poincare plot, largest Lyaponuv exponent, minimal embedding dimension, symbolic dynamic) was used. Results There wasn't a statistically significant difference in the nonlinear analysis of the heart rate variability, between the euthymic bipolar patients and controls, in the rest situation. Conclusion The nonlinear analysis of heart rate variability didn't support the notation that there is a disturbance in the autonomic nerves system of bipolar patients in the euthymic state.