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Venous hum is a benign phenomenon. At rest, 20% of the cardiac output flows to the brain via the internal carotid and vertebral arteries. This drains via the internal jugular veins. The flow of blood can cause the vein walls to vibrate creating a humming noise which can be heard by the subject. Typically, a peculiar humming sound is heard in the upper chest near the collarbone.
This may be confused with a heart murmur. The venous hum is heard throughout the cardiac cycle. The difference is easily detected by placing a finger on the jugular vein when listening to the heart, which will abolish or change the noise. A true heart murmur will be unaffected by this manoeuvre. The murmur also disappears when the patient is in the supine position or may disappear if the subject turns their head to one side. It is also known by the names "nun's murmur" and "bruit de diable" (the Devil's noise).
While a venous hum may provoke consultation with a health care professional, it is entirely harmless.