Whether prior stress increases acute stress reactivity is unresolved. The impact of life events (within the past 12 months) and social support on cardiovascular responses was investigated in 90 young male firefighters. Cardiovascular and cortisol measures were collected across baseline, arithmetic, and speech tasks; intertask recovery; and three recovery trials. Reactivity differences were not independently associated with life events. High social support was associated with greater arithmetic cardiovascular reactivity and faster recovery. Combined life events and social support grouping showed that effects of support were accentuated when event frequency was high, suggesting that life events and support interacted to sensitize future stressor responses. Support may promote the alerting response mobilization but prevent chronic allostatic load by enhancing recovery.