Dynamic fluctuations in respiratory sinus arrhythmia (RSA) were modelled throughout an emotionally challenging laboratory task, and direct associations between temporal variation in RSA responding and the deployment of specific behavioural emotion regulation (ER) strategies were assessed. Sixty-three 2- to 6-year-old children (47% girls; M[subscript age] = 46.54 months, SD[subscript age] = 12.70 months; 67% White, 6% Hispanic, 6% Asian, and 20% multiracial) exhibited ER behaviour and provided RSA data. Children's RSA exhibited U-shaped trajectories, such that RSA decreased before children implemented distraction, help-seeking, and venting behaviours, and the decline in RSA attenuated after strategies were implemented. This study is the first, to our knowledge, to concurrently couple temporal trajectories in RSA during an emotionally charged context with the onset of multiple behavioural regulation strategies. Findings significantly extend current literature by helping to elucidate the way in which parasympathetic and behavioural processes integrate in the regulation of emotion.