A relatively new technology being used to deliver academic lessons is immersive virtual reality (IVR). This study examined whether IVR is a more effective instructional medium than other multimedia, such as a video on a computer monitor. Additionally, this study explored the underlying affective and cognitive mechanisms of learning in an immersive environment. Participants viewed a history lesson in IVR or a 3D interactive video display on a desktop monitor. The results showed that participants who viewed the video lesson outperformed those who viewed the IVR lesson on transfer tests. The IVR lesson caused higher emotional arousal based on self-report and heart rate measures, and lower cognitive engagement based on electroencephalogram (EEG) measures. The results suggest that immersive environments may create excessive positive emotions, which distract form the necessary cognitive processing during the lesson, thereby harming performance on subsequent tests of learning outcomes.