interfacing to off the shelf heart rate sensors

Does anyone know how I would interface to a heartrate sensor like this:
http://www.dealextreme.com/details.dx/sku.16009 ?

It says it is digital and I am guessing that adheres to some standard that exercise machines would use. Anyone know how I would interface this to an arduino to measure and record heart rate?

There is not enough information here to say.

It has three connections so I assume it has Power +, Power - and signal. First problem is which is which. Next is it 5V? If so the data line should just connect up to a digital input pin.

That link has post indicating that the sensor is compatible with Kettler fitness equipment. You be able to find the pinouts of the connector using that information in a google search.

If not, you could try visiting a store that stocks Kettler exercise equipment. It's unlikely anyone in the shop will know, but if you bring a multimeter and a cable with a 3.5mm plug you may be able to measure the voltage on the connector to see which is +5 volts and which is ground. Its likely that ground is furthest from the tip, but either the tip or middle could be the +5 volts.

if you are asked what the heck your doing, say you may be interested in one some exercise equipment if its compatible with your computer.

If you do get some information, please post the results.

Good luck!