This is the dataset used in the 2010 Biological Psychology publication. Reference: Kok, B.E. & Fredrickson, B.L. (2010). Upward spirals of the heart: Autonomic flexibility, as indexed by vagal tone, reciprocally and prospectively predicts positive emotions and social connectedness. *Biological Psychology, 85*, 432-436. Abstract: Vagal tone (VT), an index of autonomic flexibility, is linked to social and psychological well-being. We posit that the association between VT and well-being reflects an “upward spiral” in which autonomic flexibility, represented by VT, facilitates capitalizing on social and emotional opportunities and the resulting opportunistic gains, in turn, lead to higher VT. Community-dwelling adults were asked to monitor and report their positive emotions and the degree to which they felt socially connected each day for 9 weeks. VT was measured at the beginning and end of the 9-week period. Adults who possessed higher initial levels of VT increased in connectedness and positive emotions more rapidly than others. Furthermore, increases in connectedness and positive emotions predicted increases in VT, independent of initial VT level. This evidence is consistent with an “upward spiral” relationship of reciprocal causality, in which VT and psychosocial well-being reciprocally and prospectively predict one another.