In times of need, people seek comfort and support from close others. Support provision is an integral component of attachment relationships, one that is linked with physical and psychological well‐being. Successful support provision is believed to be grounded in transactions of sensitive, caring behavior between caregivers and support seekers and to serve a profound regulatory function. However, physiological processes underlying support transactions have not been previously studied. We assessed autonomic vagal regulation and coded spontaneous emotional support behaviors in N = 100 heterosexual couples involved in a support interaction. We focused on cardiac vagal activation, operationalized as the increase in respiratory sinus arrhythmia (RSA) from baseline to interaction, as an indicator of regulatory efforts. Analyses revealed a negative association between caregivers' and support seekers' regulatory efforts, which was mediated by emotional support behaviors. We found that caregivers with greater increases in RSA from baseline to interaction provided more emotional support to their partners. Such emotional support was associated with smaller increases in support seekers' RSA and with support seekers' perceptions of their partners as being more sensitive to their needs. Finally, these links were only significant among dyads in which caregivers reported lower levels of attachment anxiety. We interpret these results in the framework of interpersonal regulatory processes, suggesting that provision of support may impose regulatory demands on the side of the caregivers, which in turn could result in attenuated regulatory efforts and positive partner perceptions for the support seekers.