In our Science chapter on "People Grow and Change" we talk about our Heart Beat and Heart Rate.  We conducted a little experiment to listen to our heart beat.  We partnered up and listened to our partners heart beat.  We had a hard time hearing it.  Then we did some exercises to get our hearts pumping.  Then we listened to our heart beat again.  It was a lot faster and louder.  We concluded that our heart rate is slower when we are just sitting or standing around.  But when we exercise our heart rate is much faster.  We also discovered when our heart rate is faster so is our breathing.