The maintenance of stable blood pressure during postural changes is known to involve integration of vestibular and cardiovascular central regulatory mechanisms. Sensory activity in the vestibular system plays an important role in cardiovascular regulation. The purpose of this study was to determine the role of vestibular gravity receptors in normal baroreflex function. Baroreflex heart rate (HR) responses to changes in blood pressure (BP) in otoconia-deficient head tilt (het) mice (n=8) were compared to their wild-type littermates (n=12). The study was carried out in conscious male mice chronically implanted with arterial and venous catheters for recording BP and HR and for the infusion of vasoactive drugs. Resting HR was higher in the het mice (661 ± 13 beats/min) than in the wild-type mice (579 ± 20 beats/min). BP was comparable in the het (113 ± 4 mmHg) and the wild-type mice (104 ± 4 mmHg). The slopes of reflex decreases in HR in response to phenylephrine (PE) were blunted in the het (-5.5 ± 1.5 beats/min/mmHg) when compared to the wild-type mice (-8.5 ± 0.9 beats/min/mmHg). Likewise, reflex tachycardic responses to decreases in BP with sodium nitroprusside (SNP) were significantly blunted in the het (-0.8 ± 0.3 beats/min/mmHg) versus wildtype mice (-2.2 ± 0.6 beats/min/mmHg). Frequency domain analysis of the heart rate variability suggests that under resting conditions parasympathetic contribution was lower in the het versus wild-type mice. Mapping of the expression of immediate early gene product, c-fos, in forebrain and brainstem nuclei in response to a blood pressure challenge showed no differences between the wild-type and het mice. These results suggest that tonic activity of gravity receptors modulates and is required for normal function of the cardiac baroreflexes.