Here are a few off the shelf products
http://store.transducersales.com/tsd200.html
http://www.ufiservingscience.com/DS10201.html
http://www.dolphinmedical.com/210adult.htm
Neither Polar or Masimo do anything like this.
Will you use an IR Led and a light sensor sensitive to IR light? Will you build a signal amplifier circuit?
There is also this Arduino sheild in development, but little info at the moment