This aim of the present study was to investigate relationships between aerobic fitness, sympathetic and parasympathetic cardiac control using pre-ejection period (PEP) and high frequency heart rate variability (HF HRV), and performance on a task requiring variable amounts of cognitive control. Fifty-six participants completed a modified-version of the Eriksen flanker task while PEP and HF HRV were collected. A graded maximal exercise test was subsequently used to measure aerobic fitness by assessing maximal oxygen uptake. Results indicated a significant relation of fitness to reaction time performance. Although no fitness differences were observed in resting state PEP or HF HRV, higher fit adults exhibited greater task-induced parasympathetic cardiac control. However, no significant mediation was found for HF HRV on the fitness-cognitive control relationship, suggesting other mediators may be important. These findings highlight the role of aerobic fitness in enhancing integrated autonomic and neurocognitive health.