The mere co-presence of another person synchronizes physiological signals, but no study has systematically investigated effects of type of emotional context and type of relationship in eliciting dyadic physiological synchrony. In this study, we investigated the synchrony of pairs of strangers, companions, and romantic partners while watching a series of video clips designed to elicit different emotions. Maximal cross-correlation of heart rate variability (HRV) was used to quantify dyadic synchrony. The findings suggest that an existing social relationship might reduce the predisposition to conform one's autonomic responses to a friend or romantic partner during social situations that do not require direct interaction.