Questions surrounding physiological interdependence in romantic relationships are gaining increased attention in the research literature. One specific form of interdependence, coregulation, can be defined as the bidirectional linkage of oscillating signals within optimal bounds. Conceptual and theoretical work suggests that physiological coregulation should be instantiated in romantic couples. Although these ideas are appealing, the central tenets of most coregulatory models await empirical evaluation. In the current study, we evaluate the covariation of respiratory sinus arrhythmia (RSA) in 32 romantic couples during a series of laboratory tasks using a cross-lagged panel model. During the tasks, men’s and women’s RSA were associated with their partners’ previous RSA responses, and this pattern was stronger for those couples with higher relationship satisfaction. The findings are discussed in terms of their implications for attachment theory, as well as the association between relationships and health.