Thearn released a free/open program for detecting and monitoring your pulse using your webcam. The code is on github for you to download, play with and modify. If this stuff takes your fancy, be sure and read Eulerian Video Magnification for Revealing Subtle Changes in the World, an inspiring paper describing the techniques Thearn uses in his code:
This application uses openCV (http://opencv.org/) to find the location of the user's face, then isolate the forehead region. Data is collected from this location over time to estimate the user's heartbeat frequency. This is done by measuring average optical intensity in the forehead location, in the subimage's green channel alone. Physiological data can be estimated this way thanks to the optical absorbtion characteristics of oxygenated hemoglobin.
With good lighting and minimal noise due to motion, a stable heartbeat should be isolated in about 15 seconds. Other physiological waveforms, such as Mayer waves (http://en.wikipedia.org/wiki/Mayer_waves), should also be visible in the raw data stream.
Once the user's pulse signal has been isolated, temporal phase variation associated with the detected hearbeat frequency is also computed. This allows for the heartbeat frequency to be exaggerated in the post-process frame rendering; causing the highlighted forhead location to pulse in sync with the user's own heartbeat (in real time).
Support for pulse-detection on multiple simultaneous people in an camera's image stream is definitely possible, but at the moment only the information from one face is extracted for cardiac analysis