ABSTRACT Age-related changes to the heart increase risk for cardiovascular disease as well as other health risks, such as frailty, falls, and dementia. Exercise helps to slow the progression of aging-associated changes to the heart and is an essential component cardiac rehabilitation (CR), which is a secondary prevention program used to speed recovery from cardiac events or surgical procedures. However, the majority of patients who enroll in CR only attend a portion of sessions and the majority that do attend fail to maintain sufficient levels of physical activity after the CR program. Anxiety is among the earliest and most intense psychological reactions following acute CVD. “Exercise anxiety”, i.e., fear and avoidance of physical activity – may be particularly relevant to successful CR. From a cognitive-behavioral framework, the presence of heart-related symptoms or comorbid conditions can heighten individuals’ awareness of bodily sensations, promote fear and worry about health and safety, and lead to exercise avoidance. We developed a manualized, theoretically-informed, cognitive-behavioral intervention called Behavioral Exposure For Interoceptive Tolerance (BE-FIT) designed to target exercise anxiety in CR patients. The fully powered parent grant (R01AG070136-01A1) includes careful examination of cognitive, behavioral and physiological mechanisms that contribute to exercise anxiety and serve as important treatment targets. Missing from the parent grant is a careful examination of deficits in information processing that reflect a bias toward threat, a core feature of anxiety pathology that can be assessed via attentional bias (AB) tasks. The literature on AB to threat has documented that anxious, compared to non-anxious, individuals exhibit threat related attentional biases across a range of anxiety disorders and there is evidence that these biases are responsive to intervention. However, relatively no work has considered how AB to exercise-related threat stimuli could influence physical activity behavior. We propose that AB towards exercise and medical- related stimuli is contextually relevant to patients in CR, and can contribute to and maintain exercise anxiety, which in turn, can undermine exercise and physical activity participation. Consistent with NOT-OD-22-140, we plan to develop and validate a new assay in order to further assessment treatment mechanism in our current RCT, and evaluate whether this mechanism is related to the intervention study’s main effect (efficacy) over the course of behavior initiation and maintenance. Specifically, we propose to develop a modified Stroop task to examine basal attentional bias to exercise threat in patients attending CR, examine its relations with validated self-report measures of fear about exercise sensations and heart-focused anxiety, and test well as whether these threat biases improve as a function of intervention. By developing and administering a novel modified Stroop task to examine threa...