Interpersonal dysfunction is a core feature of personality disorders, often affecting close relationships. Nevertheless, little is known about the moment-to-moment dynamic processes by which personality pathology contributes to dysfunctional relationships. Here, we investigated the role of physiological attunement during a conflict discussion in romantic couples oversampled for personality pathology. We hypothesized that physiological coregulation would be disrupted in individuals with personality pathology, subsequently predicting short-term discord and long-term relationship dissatisfaction. One hundred twenty-one couples completed a 10-min discussion about an area of disagreement while cardiovascular physiology and behavior were recorded. We quantified coregulation using a dynamical systems model of heart rate changes. We found that greater interpersonal problem severity was associated with more contrarian coregulation, exacerbating negative affect and interpersonal perceptions. Furthermore, the extent to which coregulation was associated with increased discord prospectively predicted relationship dissatisfaction 1 year later. Altogether, this work sheds light on a pathway by which personality pathology contributes to problems in romantic relationships. (PsycInfo Database Record (c) 2020 APA, all rights reserved).