According to a post by user "Clover" on the Nike+ support forums, Nike will be releasing a Nike+ heart rate monitor to the U.S. market on June 1, 2010. Canada will also see see a June launch date, while other international customers will see the device hitting shelves some time during the summer.
While the fifth generation iPod nano and Apple's own Nike+ iPod user guide makes reference to a Nike+ heart rate monitor, such a device has yet to surface.
Exact features, specifications, and pricing of the Nike+ heart rate monitor were not revealed. However, a good number of heart rate monitors out in the market today are priced in the $50 and higher ballpark, and many require you to use a strap across your chest in order to transmit your heart rate to an accompanying watch.