This project is at the very early brain-storming stage. This is what I need to achieve. I want to display on a monitor a flashing outline around a seated subject that corresponds to the subject's heartbeat... in real time. Can an Arduino help in any way, perhaps by translating a heartbeat microphone sound peak into an impulse to drive a graphics event in an Adobe video product (such as After Effects)?
The arduino does not have the processing power to create video. It could relay heart beat readings to a more powerful computer that does the video component. Adafruit sells this heart rate monitor that can be used to actually monitor the heart rate: Heart Rate Educational Starter Pack with Polar Wireless Sensors : ID 1077 : $65.00 : Adafruit Industries, Unique & fun DIY electronics and kits
However, if you are planning to make this into a commercial product, after the breadboarding stage, you likely will need to move from Arduinos to something that can pass the necessary certifications that can be used in health related products. I recall reading that Atmel does not certify most of its chips for anything health related. If may be less disruptive long term if you start with a platform that can meet the necessary certifications, than switching mid-stream.
Do you actually need to generate moving graphics, or is it sufficient just to vary the brightness of a fixed image? It may be as simple as using PWM to vary the brightness of a lamp that is shining through a projection slide.
The Arduino side of this would be to recognise the sound of a heartbeat. Other people have created sound pressure level displays and graphical spectrum analysers so I assume that all the capabilities you need are possible, but I have no idea how difficult it would be to pick out the sound of a heartbeat from the background noise.