Research soundtracks

http://www.freesound.org/samplesViewSingle.php?id=32424b - Hypnotic heartbeat
http://www.freesound.org/samplesViewSingle.php?id=108841 - Heartbeat

I would use this soundtrack at the very end of my opening when we see the shot of the girl tied up to the chair. I think this soundtrack would work well as it could represent her heartbeat increasing. As the camera slowly works its way up her body using close ups , the heartbeat would increase giving the audience the illusion that she's becoming more and more frantic.

http://www.freesound.org/samplesViewSingle.php?id=107356

This soundtrack I would use to show the tension in the car as the two criminals wait for their victim .The ticking of the clock reinforces the fact that they are waiting and causes the audience to feel anticipated.

http://www.freesound.org/samplesViewSingle.php?id=102722

This sound effect of a car boot shutting I would use as the car boot closes as the shot cuts to a black background with the title of the film appearing. The effect of the exaggerated sound is that its very loud and definate , it causes the audience to be threatened.