The paper examines the physiological response – as manifest as heart rate changes – and subjective impressions of presence, of a group of players of 1st Person Simulations. Varied experimental factors include two different simulations – VBS1 and Joint Ops: Typhoon Rising, solo and multi-player team play, and different types of scenarios. Across the population heart rate increase from resting to game play was found to be relatively minor – far less than the increase for light exercise (walking). However physiological response to game play was found to be highly individual with two subjects showing an actual drop in heart rate, while one showed a very significant increase. Subjective impressions of presence, obtained via questionnaire, showed that players were significantly engaged with the game. However no correlation existed between subjective measures and heart rate changes. Differences in game setting – game engine, solo versus multi-player - manifested as relatively minor differences in objective (heart rate) and subjective (questionnaire) measures.