Introduction Syncope is defined as transient loss of consciousness, due to decrease in brain perfusion. The most frequent mechanism is vasovagal syncope. In many patients, the cause of syncope remains unspecified, despite an extensive diagnostic work-up. Tilt-test (TT) is an acknowledged diagnostic tool for syncope. Currently, the so-called Italian protocol of TT is most widely used. Vasovagal syncope is caused by impaired circulatory regulation in response to orthostatic stress. One of the available tools to examine the influence of the nervous system on the circulation is the analysis of heart rate variability (HRV). Despite numerous publications concerning HRV parameters and autonomic regulation in patients with syncope, direct comparisons and metaanalysis of the results is impossible, due to variability of TT protocols and study group specifications. Aim of the study As there is no uniform model of HRV during TT, we aimed to analyze HRV parameters during TT (performed according to the Italian protocol) in patients with vasovagal syncope, in order to determine the possible application of HRV measurements in clinical practice in that group of patients. Detailed objectives were: (1) analysis and comparison of HRV in patients with and without the history of syncope; (2) analysis of HRV changes in consecutive stages of TT; (3) identification of possible HRV differences between patients with positive and negative TT results. Materials and methods Patients between 18 and 50 years of age were qualified for the study, if they had a history of at least 2 incidents of syncope or presyncope within the preceeding 6 months, and if signs and symptoms indicated the vasovagal mechanism. The study group included 150 patients: 100 consecutive patients with a postive TT result (POS), and 50 consecutive patients with a negative TT result (NEG). The control group (CG) comprised 50 volunteers with no history of syncope nor presyncope, matched according to age and sex to the study group. In all patients a TT was performed according to the Italian protocol, with paced breathing at a rate of 15/min. Time-domain (meanRR, SDNN, RMSSD, pNN50) and frequency-domain (abs_LF, abs_HF, rel_LF, rel_HF, norm_LF, norm_HF, LF/HF) HRV parameters were analyzed and compared at different stages of TT in the study groups as specified above. Results 100 patients at the age of 18-44 years were included in the POS group, 50 patients at the age of 18-39 years in the NEG group, and 50 volunteers at the age of 20-39 in the CG. Volunteers in the control group developed unexpectedly high percentage of positive TT (14 patients). For consistency of analysis, the CG was thus subdivided according to the result of the TT into CG_POS (positive result of TT) – 14 patients, and CG_NEG (negative result of TT) – 36 patients. Based on HRV analaysis, no significant differences in HRV values were noted between patients with a history of syncope and positive or negative result of TT. Upright tilt resulted in HRV changes of the same direction and value in syncopal patients in the POS and NEG goup, as well as in patients in the CG_NEG group. Conclusion HRV values and changes of those values at subsequent stages of TT were not different between syncopal patients with postive or negative TT result, or negative TT control group. The Italian protocol of TT may be associated with a surprisingly high percentage of false positive results.