The "mediated sense of presence'' is a technology-induced illusion of being present in one (simulated) place when one is actually present in another (physical) place. Typically experienced in virtual worlds, mediated presence is generated by different technological, cognitive, and emotional factors. The aim of this study was to test how to optimise the virtual experience by manipulating some of these factors. Specifically, we tested if an immersive technology and/or a meaningful narrative context influence the users' sense of presence, providing a more compelling experience than a non-immersive and non-contextualized virtual space. Eighty-four students, randomly divided into four groups, were asked to find a blood container inside a virtual hospital in an immersive or non-immersive condition and with or without an emotionally related narrative. Two presence questionnaires and heart-rate variations were used to measure the effects of the four conditions on the users' sense of presence. Results showed a significant effect of narrative, F(8, 73)=30.346, p < 0.001, and level of immersion, F (8, 73)=10.913, p < 0.001, and a significant interaction between narrative and immersion, F(8, 73)=2.062, p=0.05, both on the presence questionnaires and on the heart-rate variations. Moreover, considering the factors immersion (I) and narrative (N) together, we found that the I-N condition generated the highest level of presence. We argue that both immersion and narrative are important in creating an effective virtual reality experience because they contribute differently to increasing the sense of presence. Immersion increases the place illusion, while the narrative contributes to generating an emotional response and strengthening the subjects' sense of inner presence.