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Spectral components of cardiovascular oscillations are related to complex autonomic control mechanisms. Since these oscillations are non-stationary, time-frequency (T-F) analysis has been used in studying cardiovascular oscillations such as variabilities of heart rate and blood pressure; however, few studies have extended the T-F analysis to other cardiovascular signals such as pulse transit time (PTT). In this preliminary study, a T-F analysis method based on a time-variant autoregressive model was used to study the beat to beat spectra of R-R interval (RRI) of electrocardiogram, systolic blood pressure (SBP) and PTT on 8 normotensive subjects after exercise. It is observed from the results that spectra of RRI, SBP and PTT comprised of two distinguished components in the 0.03-0.15 Hz and 0.18-0.4 Hz respectively and that the spectra of SBP and PTT were relatively similar compared to spectra of RRI. However, the beat to beat power spectral densities (PSD) of the signals were not the same all the time. Furthermore, a physiological mechanism-based model was proposed for the generation of ECG, BP and PPG signals, and to interpret the phenomena observed in experiments. Further investigation is needed to quantify this similarity and to study the inherent correlations and mechanisms mediating these cardiovascular oscillations.