What about making an MC of the "beat" (I presume you mean a heart beating, not an ECG readout?), and script it so that you can set the timing in between "beats" (the movieClip playing). For example, make the beat last 1/4 of a second (3 frames at 12 fps), and set an interval between each beat as 1/4 of a second (or thereabouts - it won't be exact) by using getTimer() to retrieve the number of milliseconds passed / 1000.
You could even make it more "realistic" by creating a beat interval and a pulse interval ... when the heart beats you get 2 beats close together, one for blood in and one for blood out, don't you? then there's a longer gap in between pulses. So set 2 wait periods, the second longer the the first, and alternate between the two!
I should really get a life now, shouldn't I ... ?
If you want any help, let me know and I'll see if I can come up with anything. Right now I'll just shuffle back into my box :/
