PURPOSE: Heart rate variability (HRV) is a noninvasive and sensitive method used to evaluate autonomic function of the heart based on specific polysomnographic parameters. This study aimed to determine the effect of expansion sphincter pharyngoplasty (ESP) on HRV and the apnea-hypopnea index (AHI) in patients with obstructive sleep apnea (OSA). MATERIALS AND METHODS: This retrospective cohort study included patients who presented to the Department of Otorhinolaryngology, Hacettepe University Hospital (Ankara, Turkey), were diagnosed with OSA, and underwent ESP. Patient medical records, including demographic data, polysomnographic findings, and HRV parameters, were reviewed. The predictor variable was the effect of ESP on the AHI and the primary outcome variables were HRV parameters. Descriptive and bivariate statistics were computed using chi(2) test, t test, and Mann-Whitney U test. RESULTS: The mean age of the 28 patients (20 men and 8 women) was 43 +/- 9.9 years. Surgical success (AHI, <20; 50% decrease in the AHI) was achieved in 16 patients (57.1%). The AHI decreased in 22 patients (78.6%) but increased in 6 patients (21.4%) after ESP. The ratio of low-frequency power (LF) to high-frequency power (HF) decreased significantly in the patients with successful surgery and in those whose AHI decreased after surgery (P = .02 and P = .001, respectively). For the change in the LF/HF ratio, 19 patients had a decrease in sympathetic activity, whereas 9 had an increase in sympathetic activity, after ESP. A decrease in sympathetic activity after ESP was significantly associated with surgical success and a decrease in the AHI (P = .033 and P = .001, respectively). CONCLUSION: ESP is an effective surgical option for the treatment of OSA and lowers the AHI. Successful ESP plays a role in decreasing sympathetic activity of the heart, which might be associated with a decrease in the risk of cardiovascular disease.