OBJECTIVE: Reduction in carotid artery wall elasticity may interfere with baroreceptor function that could lead to low vagal tone. We studied at the population level the relations between carotid-artery-distensibility (Cdist) and vagal modulation of heart rate. METHODS AND RESULTS: Cdist was assessed with ultrasonic measurements of changes in carotid artery diameter during cardiac-cycle. Vagal tone was estimated with the heart rate variability (HRV) in 1872 healthy 24-39year-old subjects. Cdist was significantly related with all HRV-components (always P<0.0001). After adjustments with sex, age and heart rate, we found statistically significant correlation between Cdist and the high-frequency component (HF, estimate of vagal-tone) of HRV (P<0.05). An inverse association between the number of cardiovascular risk-factors and vagal-tone was seen in subjects with less elastic arteries, but not in subjects with more elastic arteries (P for interaction=0.01). CONCLUSIONS: These data support the hypothesis that reduction in carotid artery wall elastic properties may lead to low vagal tone. Furthermore, carotid distensibility seemed to modify the relation between risk-factors and HRV. Increased cardiovascular risk associated with low vagal tone may partly be mediated via changes in carotid artery elastic properties.