the present study sought to explore the ability of a single session of heart rate variability biofeedback (hrv bf) to mitigate the negative responses to a social comparison challenge. one hundred and fourteen undergraduate females were randomly assigned to one of three conditions: high-hrv bf, low-hrv bf, and no-bf. following a single 15-min bf session, whereby they followed their assigned instructional set, participants viewed fashion magazine images while instructed to compare themselves to the models based on appearance characteristics. consistent with previous findings, the social comparison challenge increased negative mood and body dissatisfaction across the sample as a whole. the effect of the social comparison challenge on negative mood was moderated by dispositional body concerns, with those higher on this dimension experiencing greater negative mood after viewing the images. in addition, time spent engaged in social comparison processing was related to more negative responses. the main finding indicated that hrv bf was not effective in reducing negative reactions for the average participant; however, resting hrv moderated the effectiveness of the intervention. specifically, those with low intrinsic hrv benefitted the most from the hrv bf and experienced the least negative mood reactivity in response to the images. results are discussed in terms of their relevance to the social comparison literature as well as to the future implementation and application of hrv bf.