BACKGROUND: Heart rate variability (HRV) is discussed to signal social safety. Conversely, shyness might be accompanied by attenuated feelings of social safety. This study aimed to examine if shy individuals show compromised HRV in everyday life and if social interactions with close others (both face to face and computer-mediated) might moderate this association. METHODS: Social interactions and HRV (root mean squared successive differences) were recorded across three consecutive days in 51 participants. FINDINGS: HRV was lower in shy as compared to non-shy individuals. When interacting with close others, HRV in shy individuals increased considerably, while there was no effect for non-shy individuals. Exploratory analyses confirmed that effects were more reliable for face-to-face as compared to computer-mediated interactions. DISCUSSION: Shyness may be associated with compromised social engagement as indicated by lower HRV. However, shy individuals may benefit from face-to-face interactions with close others, thus suggesting a buffering effect on cardiac function.