In this study we created a virtual 3D world for learning to manage medical emergencies and evaluated it with 24 high school students in the USA and Sweden. We found that students in both groups felt immersed and found the online simulation easy to use. Scores for flow and self-assessed flow were significantly higher for the RHS group as compared to the HG group (p=.001 and .023 respectively; Mann Whitney U test). Self-efficacy scores for the HG group were significantly higher after training (p=.016 Mann Whitney U test). Males in the RHS group scored significantly higher on flow and self assessed flow than females (p=.006 and p=.023 respectively; Mann Whitney U test). This study demonstrates the potential value of using MMOS for learning to respond to medical emergencies.