Although the so-called low-frequency (around 0.1Hz) components of heart rate variability are an accepted marker of sympathetic activity to the heart and the circulation, their origin remains elusive. In order to characterise the frequency response of the heart and the vessels to the stimulation of the arterial baroreceptors we applied the neck suction technique with a sinusoidal function at different frequencies, and studied the changes in the cardiovascular system. In all subjects the neck suction induced RR interval oscillations at both low- (0.10Hz) and high (0.20Hz) frequencies, but with greater response at 0.1Hz, while blood pressure and skin blood flow oscillations responded only at low frequency (low-pass behaviour). To assess whether this kind of response could have played a role in the genesis of spontaneous LF fluctuations we studied the changes induced by an impulsive neck suction during post-expiratory apnoea: if the LF were due to a resonance in the baroreceptor loop, a single perturbation of the cardiovascular system would have produced oscillations in the cardiovascular system similar to those observed spontaneously. We found that, after the suction, a damped oscillation (whose period was similar and correlated to that of the spontaneous LF) was generated in the cardiovascular system, suggesting that the LF could be indeed generated by a peripheral mechanisms, primarily involving the baroreceptors. In further support of this hypothesis, we also found that counteracting the respiratory fluctuations in blood pressure by appropriately timing a sinusoidal neck suction, we significantly reduced not only the respiratory fluctuations in RR interval, but also the LF. Nevertheless, during undisturbed apnoeas, we observed spontaneous oscillations in the LF range (though slower than those observed during breathing). This observation contrasts with the hypothesis that a resonance in the cardiovascular system is the only source of the LF fluctuations, (since after removing the effects of respiration the LF should disappear as well) and suggests the contemporary presence of other factors, such as a central oscillator, tuned at a similar frequency. In conclusion, the arterial baroreceptors exert a strong, though probably not exclusive influence on the cardiovascular fluctuations, through both sympathetic and vagal activity; the LF appears to be generated not only by a resonance in the cardiovascular system, but also by other independent factors, such as a central oscillator.