A Nike+iPod compatible heart rate monitor is expected to launch June 1, according to a posting on the Nike+ support forums. A “Nike+ Pro” member claimed, in response to a question regarding a menu item for the Heart Rate Monitor on an iPod, that the device will launch in the U.S. on June 1, “although it may reach some retail outlets slightly sooner.” The post goes on to say that the monitor will reach Canadian markets later…