OBJECTIVE: High frequency (HF) heart rate variability (HRV) has long been accepted as an index of cardiac vagal control. Recent studies report relationships between HF-HRV and indices of positive and negative affect, personality traits and well-being but these studies generally are based on small and selective samples. METHOD: These relationships were examined using data from 967 participants in the second Midlife in the U.S. (MIDUS II) study. Participants completed survey questionnaires on well-being and affect. HF-HRV was measured at rest. A hierarchical series of regression analyses examined relationships between these various indices and HF-HRV before and after adjustment for relevant demographic and biomedical factors. RESULTS: Significant inverse relationships were found only between indices of negative affect and HF-HRV. Relationships between indices of psychological and hedonic well-being and positive affect failed to reach significance. CONCLUSIONS: These findings raise questions about relationships between cardiac parasympathetic modulation, emotion regulation, and indices of well-being. (PsycINFO Database Record