Most of the studies on the effect of trait positive affect (PA) and cardiovascular activity have focused on heart rate (HR) and blood pressure (BP) rather than heart rate variability (HRV). However, trait PA might sustain homeostasis for the autonomic system (ANS) by reducing activity in the sympathetic system (SNS) and increasing the activity in the parasympathetic system (PNS). A common index for the PNS is the vagal tone measured indirectly through HRV. The present study assessed whether trait PA influences cardiovascular response to various stress tasks by monitoring participants’ HRV measured by RMSSD (root mean square of successive differences) along with HR and interbeat interval (IBI). A total of 54 participants performed various cognitive tasks and Trier Social Stress Tasks while their vital signs were monitored, and trait PA was measured with PANAS. The cognitive tasks included both high- and low-stress tasks, including fatigue-inducing 20 min Stroop tasks. The results showed overall higher HRV as measured by RMSSD for participants who have higher levels of trait PA, indicating more PNS activity compared with low-trait-PA individuals, particularly at the end of the task performance during the fatigue induction. High-trait-PA individuals also had a lower HR during the fatigue-inducing task and a higher IBI. The results support previous work by further indicating a more adaptive response and consequently better emotional regulation for high-trait-PA individuals in a complex, prolonged task setting.