Background Borderline Personality Disorder involves strong interpersonal disruptions, often associated with early maltreatment. However, the individual capacities which alter BPD-related interpersonal problems are unclear. Here, we examine two contributors to interpersonal functioning: interoceptive accuracy and parasympathetic activity. Interoceptive accuracy is the ability to correctly perceive body states, such as how quickly one’s heart is beating, and has been associated with emotional experience and various crucial social capacities. Similarly, parasympathetic activity is related to social processing and inhibition of impulses. As such, both may contribute to BPD interpersonal symptoms, albeit different types of interpersonal problems. Method Sixty-five individuals completed the Inventory of Interpersonal Problems and the Millon Clinical Multiaxial Inventory followed by a task to assess interoceptive accuracy, the heart rate monitoring task, in which participants counted their heartbeats while concurrent physiological data was recorded; and an assessment of vagal tone, used as an index of regulatory flexibility. Results Participants who reported poor interpersonal boundaries, consistent with borderline personality disorder styles, had worse interoception, whereas those high in aggression had lower vagal tone. Borderline personality symptoms overall were related to IA and significantly to vagal tone. Conclusions These findings suggest that interoceptive accuracy is associated with interpersonal problems, where people are overly influenced or enmeshed with others, possibly to compensate for the absence of their physical and emotional awareness.