Anxiety is marked by impaired inhibition of distraction (Eysenck et al., 2007). It is unclear whether these impairments are reduced or exacerbated when loading working memory (WM) with non-affective information. Cardiac vagal control has been related to emotion regulation and may serve as a proxy for load-related inhibition under anxiety (Thayer and Lane, 2009). The present study examined whether: (1) the enhancing and impairing effects of load on inhibition exist together in a nonlinear function, (2) there is a similar association between inhibition and concurrent vagal control, (3) nonlinear relations depend on trait anxiety. During anxiogenic threat-of-noise, 116 subjects maintained a digit series of varying lengths (0, 2, 4, 6 digits) while completing a visual flanker task. The task was broken into four blocks, with a baseline period preceding each. ECG was acquired throughout to quantify vagal control as high-frequency heart rate variability (HRV). There were significant quadratic relations of WM load to flanker performance and to HRV, but no associations between HRV and performance. Trait anxiety did not moderate any relations among HRV, load, and inhibition. Results indicate that low load was associated with relatively better inhibition and increased HRV. Findings suggest that attentional performance under anxiety depends on the availability of WM resources, which might be reflected by vagal control. These results have implications for treating anxiety disorders, in which emotion regulation can be optimized for attentional focus.