I thought this might be of interest considering the topic. I just ordered a pulse oximeter for my father. It measures oxygen concentration in the blood as well as heart rate. I read about coaches using them with swimmers.
I got a good deal on a meter, maybe because it's pink. heh Only 35.15 USD after using a 5% off coupon code. Free shipping. I doubt that it's water-proof though.
Pulse oximeter: http://www.clinicalguard.com/fingert...dlp-p-161.html
The coupon codes are listed here: http://www.tjoos.com/Coupon/113822/ClinicalGuard.com
BTW, the word "pulse" doesn't refer to heart rate. It has to do with the way that the meter reads arterial blood flow.
I'd really like to play with one, but I can't even afford $35. T_T