Heart Flow 639 Hz For Deep Sleep [8 Hours]

A full night of 639 Hz. Warm, steady, and quiet enough to leave on while you sleep. This eight-hour tone is for the evenings you want the day to drop away, a soft hold in the room from bedtime through sunrise. Keep the volume low. The frequency stays with you the whole way, so you can fall in at lights-out and still have it there if you surface before morning.