Cardioventilatory coupling (CVC) is a temporal alignment between the heartbeat and inspiratory activity and is a major determinant of breath-to-breath variations in observed respiratory rate (f_o). The cardiac-trigger hypothesis attributes this to adjustments of respiratory timing by baroreceptor afferent impulses to the central respiratory pattern generator. A mathematical model of this hypothesis indicate that apparent CVC in graphical plots of ECG R wave, to inspiratory times is dependent on the heart rate (HR), rate of the intrinsic respiratory oscillator (f_i), as well as the strength of hypothetical cardiovascular afferent impulse. Not accounting for HR and f_i may explain why previous attempts to identify the neural pathways involved in CVC produced inconsistent results. Cognizant of these interactions, we examined the role of the vagus nerve and arterial baroreceptors in CVC, factoring in the ratio between HR and f_i by cardiac pacing 29 anesthetized Sprague-Dawley rats and incrementally changing the HR. Assuming a relatively constant f_i, this enabled the examination of CVC across a range of HR/f_o values before and after vagotomy, sino-aortic denervation, and vago-sino-aortic denervation. We confirmed the relationship between CVC, HR/f_o ratio and breath-to-breath respiratory period variability, and demonstrated the loss of these relationships following baroreceptor elimination. Sham experiments (n=8) showed that these changes were not due to surgical stress. Our data support the notion that inspiratory timing can be influenced by cardiac afferent activity. We conclude that the putative cardiovascular input arises from the arterial baroreceptors and that the vagus nerve is not critical for CVC.