With many industrialized societies bearing the cost of an increasingly sedentary on the health of their populations there is a need to find new ways of encouraging physical activities to promote better health and well being. Exergaming is a term used to describe video games that also provide exercise as part of the experience and is thus a possible means of encouragement, particularly for an audience that may be reluctant to undertake more conventional forms of exercise. With the increasing power of mobile phones and the recent emergence of personal heart rate monitors, aimed at dedicated amateur runners, there is now a possibility of enabling Mobile Exergaming incorporating real-time physiological data along with other general fitness applications designed to promote well being. In this paper we present a novel heart rate and movement controlled Mobile Exergame inspired by the old arcade classic Space Invaders which we have termed Health Defender which forms part of a general health monitoring software for mobile phones called Heart Angel. Player experience shows the potential for mobile exergaming and that as the technology becomes more prevalent is a real possibility for improving health and well being.