The fifth Korotkoff sound, K5, represents the diastolic pressure. Korotkoff sounds are the series of sounds medical professionals listen for when measuring blood pressure using a sphygmomanometer. These sounds correlate to different phases of blood flow through the artery as pressure is released. The disappearance of the Korotkoff sounds signifies the diastolic pressure, the pressure in the arteries when the heart rests between beats.