We investigate interpretations of a biosignal (heartrate) in uncertain social interactions. We describe the quantitative and qualitative results of a randomized vignette experiment in which subjects were asked to make assessments about an acquaintance based on an imagined scenario that included shared heartrate information. We compare the results of this experiment in adversarial and non-adversarial contexts of interaction. We find that elevated heartrate transmits cues about mood in both contexts, but that these cues do not appear to impact assessments of trustworthiness, reliability and dependability. Counter to our expectations, we find that normal (rather than elevated) heartrate leads to negative trust-related assessments, but only in an adversarial context. Our qualitative analysis points to the role of social expectations in shaping contextual interpretations of heartrate, and reveals individual differences in the way interpretations are constructed. We unpack some of the ways that social meanings can arise from biosensor data, and discuss considerations for those designing interactions with wearables.