Theoretical accounts of autism have hypothesized links between arousal and behavior, but research translations of theory to real-world contexts have been limited. In this single-subject experimental analysis, a school-age subject chose between high and low arousing activities with real-time monitoring of behavior and heart rate (HR). Time series statistical analysis showed significant changes in HR associated with activity type and no association with motor movement. Sequential analysis showed that activity choice and HR were significantly associated (i.e., activity choice sequentially dependent with the preceding level of HR). Highly arousing activities were more likely to be chosen following high HR and vice versa. Results provide evidence of the feasibility of an integrative biobehavioral approach to understand behavior in neurodevelopmental disorders.