Worry is the defining feature of generalized anxiety disorder (GAD), and rumination is a central process in depression. GAD and depression are highly comorbid, and worry and rumination reflect similar perseverative cognitive processes. Prior studies have largely assessed these emotion regulation strategies at the trait level, which has resulted in a limited understanding of their phasic characteristics, including associated physiological processes. We addressed this limitation by examining the relationship between spontaneous state-level worry and rumination and heart rate variability (HRV)-a physiological measure of emotion regulation-in response to emotion-eliciting film clips. We found differential associations between worry and rumination in relation to HRV, such that, worry was more consistently associated with HRV across emotional contexts than rumination was. Findings highlight functional distinctions between worry and rumination that have implications for understanding their associations with mood and anxiety disorders and, more broadly, for theories of emotion regulation and psychopathology.