Three types of carotid sinus (CS) syndrome have been described: cardioinhibitory, vasodepressor and mixed. For the treatment of symptomatic patients with associated significant cardioinhibition, permanent ventricular demand pacing systems are often implanted. Even with this pacing modality, some patients remain symptomatic because of continued (and at times aggravated) vasodepression. This study assesses the effects of loss of atrial preloading and orthostasis after carotid massage in patients with CS hypersensitivity. Eleven patients were studied using constant intra-arterial pressure measurements during either ventricular (VVI) or atrioventricular sequential (DVI) pacing in both supine or upright positions. The measurements performed included the magnitude of decrease in arterial blood pressure (BP), the rate of decrease of BP and the percent change in BP from baseline values. After carotid massage, all 11 patients had greater hemodynamic change with the VVI than DVI pacing mode, whether in the supine or upright position. The decreases in systolic BP were: DVI (supine) 29 mm Hg, VVI (supine) 48 mm Hg, DVI (upright) 37 mm Hg, and VVI (upright) 59 mm Hg (mean group values, p less than 0.001). The rates of decrease of systolic BP were: DVI (supine) 2.9 mm Hg/s, VVI (supine) 5.7 mm Hg/s, DVI (upright) 4.1 mm Hg/s, and VVI (upright) 8.3 mm Hg/s (mean group values, p less than 0.001). VVI pacing, particularly in the upright position, resulted in a significant increase in the incidence of patient symptoms (p = 0.03). Thus, in CS hypersensitivity, VVI pacing results in significant hemodynamic deterioration compared to DVI mode. This aggravation of the vasodepressor component results in increased patient symptoms, and therefore, DVI is the optimal pacing mode.