ObjectiveTo investigate autonomic function changes in patients with neurally mediated syncope.MethodsWe collected the clinical data of patients presenting with syncope or presyncope. According to the results of head-up tilt test (HUTT), they were divided into an HUTT positive (mixed type) group and an HUTT negative group, each with 53 cases. Each heart rate variability (HRV) index of the two groups were comparatively analyzed before HUTT and during the testing.ResultsBefore the testing, there were no statistically significant differences in the HRV time-domain indexes of SDNN, SDANN, SDNN index, rMSSD, pNN50, and TINN between the two groups (all P> 0.05); there were also no statistically significant differences in the HRV frequency-domain indexes of LF, HF and LF/HF between the two groups (all P> 0.05). During the process of HUTT, if the during-HUTT indexes were compared between the two groups, it revealed that rMSSD value of the HUTT positive (mixed type) group was significantly higher than that of the HUTT negative group (P< 0.05).ConclusionCompared to pre-HUTT HRV indexes, during-HUTT HRV indexes demonstrate greater clinical significance. The presence of vagal overactivity immediately at the onset of syncope in patients with neurally mediated syncope.