Burnout, a pathological consequence of chronic work stress, shows an increasing incidence rate in industrialized countries. Previous findings indicate that burnout may be linked to a detachment of the negative association between subjectively appraised task demand and cognitive performance, which is typically seen in healthy individuals. The present study sought to confirm this relationship and to investigate whether this dissociation is mirrored in a biological marker of self-regulation, i.e., resting vagally mediated heart rate variability (HRV). A heterogeneous sample (N = 65) of working adults (M age = 43.3, SD = 10; 23.1 % male) with varying degrees of burnout symptomatology completed three cognitive tasks (2-back, number-letter, and go/nogo) to assess different domains of executive functioning (updating, set-shifting, and inhibition), and respective demand ratings. Additionally, vagally mediated HRV at rest, operationalized as the root-mean square differences of successive R-R intervals (RMSSD), was recorded. Burnout symptomatology moderated the association between subjective task difficulty and performance parameters of the go/nogo task, such that higher burnout scores were associated with reductions in the naturally occurring negative association between self-rated task demand and response inhibition. Intriguingly, this pattern was mirrored when replacing burnout with HRV. These findings suggest that burnout symptomatology, and individual differences in self-regulatory capacities (indexed by resting HRV), may alter ones capacity for accurate task evaluation, a mechanism which could potentially underlie the dissociation between self-rated cognitive function and actual performance among individuals experiencing burnout.