Purpose: The heritability of the response to exercise training in resting blood pressure (BP) and heart rate (HR) was assessed in 482 Caucasian individuals comprising 98 families participating in the HERITAGE Family Study. Methods: All individuals were sedentary at the baseline visit (time 1 measurement). After completing a 20-wk exercise-training program, subjects were measured again (time 2). A familial correlation model was used to assess the heritability (genetic plus familial environmental) of the response in resting systolic BP (SBP), diastolic BP (DBP), and HR, computed as the difference between the two measurement times. This response was adjusted for the effects of baseline levels and age within sex and generation groups. Analyses were conducted separately in a subsample of families in which at least one family member was considered to have elevated BP (95th percentile; SBP ≥ 135 or DBP ≥ 80). Results: Several novel findings emerged from this study. First, the SBP and HR response may be influenced by genetic factors. The maximal heritabilities were 20% (SBP) and 36% (HR) in the elevated BP, 18% and 24% in the complete, and not significant in the normotensive samples. For DBP, there were cohort effects (significant sibling and spouse but not parent-offspring correlations) in the complete and normotensive samples that may be due to generation-specific environmental influences. Conclusion: The trainability of SBP and HR in families with elevated BP appears to be determined in part by genetic factors, whereas DBP trainability may be more a function of environmental effects.