Heart rate timer

[Tricia PORTER]

I'm trying to develop a "Heart Rate Timer" like the one displayed at the bottom of this site: http://www.creativewindows.simplenet.com/page3.html   It's just a displayed timer that you can start to check your pulse for 60 seconds.  Can someone give me a hint on how to do this?  I just need the basics to get started, and then I'll be able to figure it out.  Thanks!  All help is very much appreciated.