There is uncertainty as to how high-frequency heart rate variability (HF-HRV), a marker of an individual\'s capacity for flexible physiological reactivity, relates to an individual\'s tendency to experience negative emotions. We propose that both excessively high and excessively low HF-HRV may reflect maladaptive physiological reactivity tendencies associated with high negative affectivity and that this association may be influenced by the use of emotion regulation strategies, such as cognitively reappraising negative environmental stimuli to downregulate the experience of negative emotions. The purpose of the current study was to examine the moderating role of cognitive reappraisal in the quadratic association between HF-HRV and negative affectivity. Electrocardiograms (ECG) were recorded at rest for 269 young adults (77% female; M = 19.7 years) who then completed self-report rating scales assessing trait negative affectivity and trait cognitive reappraisal. As predicted, high and low HF-HRV were associated with high negative affectivity at low levels of trait cognitive reappraisal. At high levels of trait reappraisal, the quadratic association between HF-HRV and negative affectivity was not significant. These results suggest that, contrary to traditional views, high HF-HRV may not always be an adaptive characteristic and may depend on an individual\'s use of emotion regulation strategies, such as cognitive reappraisal.