The current study examined cardiac and behavioral responses to changing auditory and visual information while using modified oddball tasks. When instructed to press the same button for auditory and visual oddballs, auditory dominance was found with cross-modal presentation slowing down visual response times and decreasing visual accuracy. When instructed to make separate responses to auditory and visual oddballs, visual dominance was found with cross-modal presentation slowing down response times and decreasing auditory accuracy. However, examination of cardiac responses that were time-locked to stimulus onset show cross-modal facilitation effects, with discrimination of oddballs and standards occurring earlier in the course of processing in the cross-modal condition than in the unimodal conditions. These findings shed light on potential mechanisms underlying modality dominance effects and have implications on tasks that require simultaneous processing of auditory and visual information.