Two symbolic indices, i.e. the percentage of sequences characterized by three heart periods with no significant variations (0V%) and that with two significant unlike variations (2UV%) have been found to reflect changes in sympathetic and vagal modulations respectively. We tested the hypothesis that symbolic indices may track the gradual shift of the cardiac autonomic modulation during an incremental gravitational stimulus. Symbolic analysis was carried out over heart period variability series (250 cardiac beats) derived from ECG recordings during graded head-up tilt test (0, 15, 30, 45, 60, 75, 90°) in 17 healthy subjects. The percentage of subjects showing a significant linear correlation (Spearman rank order correlation) with tilt angles was utilized to evaluate the performance of symbolic analysis. Spectral analysis was carried out for comparison over the same series. Symbolic index 0V% progressively increased with tilt angles, while 2UV% gradually decreased. The decline of 2UV% was larger than the increase of 0V% at low tilt angles. Both 0V% and 2UV% were linearly correlated with tilt angles in a percentage of subjects larger than any spectral index. Our findings suggest that symbolic analysis performed better than spectral analysis, thus being a suitable methodology to assess the subtle changes of cardiac autonomic modulation induced by graded head-up tilt test. Moreover, symbolic analysis indicates that the changes of cardiac sympathetic and vagal modulations observed during this protocol were reciprocal but characterized by different absolute magnitudes.