Interpersonal Cardiac Synchrony During Emotional Sharing Between Strangers

Interpersonal physiological synchrony is well-documented in close relationships, where it supports social bonding and emotion regulation; however, little is known about whether cardiac synchrony emerges during emotional interactions between strangers. Here we examined interpersonal cardiac synchrony in pairs of strangers during an emotional sharing task. Eighty participants (40 dyads) engaged in 15 minutes of emotional sharing, during which one participant recounted a negative personal experience while the other provided support. We assessed cardiac synchrony as the cross-correlation of residualized inter-beat interval (IBI) time series from synchronized electrocardiogram (ECG) recordings. Results showed that greater mutual liking, gender match, and shared emotional perception were linked to stronger cardiac synchrony, suggesting that interpersonal synchrony reflects social and emotional alignment even between strangers. Additionally, the similarity between the heart rate variability (HRV) of each interaction partner predicted greater synchrony, indicating that physiological compatibility may facilitate alignment. We also examined whether a brief mindfulness induction given to the support provider enhanced synchrony and interaction quality. However, the mindfulness induction had no significant effect, suggesting that a brief self-regulation practice may not influence physiological alignment in first-time interactions. These findings extend research on interpersonal cardiac synchrony beyond established relationships, identifying key factors that shape physiological alignment during emotional sharing in first-time interactions.