Cardiovascular regulation involves feedback and feedforward limbs of a control loop. In order to understand the behavior of this control system, it is desirable, although difficult, to disentangle the dynamical properties of the feedback and feedforward limbs. The authors have developed a conscious animal model in which the control loop is functionally opened by interruption of atrioventricular conduction, thereby dissociating fluctuations in cardiac output and arterial pressure from reflexogenic changes in atrial rate. Cross-spectral techniques are used to compute the frequency response of the mechanical system that couples ventricular activity to arterial pressure and of the baroreflex system that governs sinoatrial rate. The infusion of various pharmacologic agents is used to study the behavior of the system under conditions of selective autonomic blockade. Results from this work will enable validation of analysis techniques that attempt to derive open-loop system properties from data collected in closed-loop preparations.