Webster's New World Medical Dictionary

vasovagal syncope
The temporary loss of con-
sciousness in a particular kind of situation (situa-
tional syncope, or fainting) due to a vasovagal
reaction. See also 
syncope.
VBAC
Vaginal birth after caesarean section. See
caesarean section, vaginal birth after.
VDRL test
Venereal Disease Research Laboratory
test, a blood test for syphilis. A negative (nonreactive)
VDRL test is compatible with a person not having
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VDRL test
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syphilis. However, a person may have a negative
VDRL and still have syphilis because in the early
stages of the disease, the VDRL often gives false neg-
ative results. The VDRL test is sometimes positive in
the absence of syphilis. For example, a false positive
VDRL can be encountered in a patient with infec-
tious mononucleosis, lupus, antiphospholipid anti-
body syndrome, hepatitis A, leprosy, malaria, and,
occasionally, pregnancy. See also 
syphilis.
vector
In medicine, a carrier of disease or of
medication. For example, in malaria a mosquito is
the vector that carries and transfers the infectious
agent. In molecular biology, a vector may be a virus
or a plasmid that carries a piece of foreign DNA to a
host cell.
VEG-F
Vascular endothelial growth factor.
vein
A blood vessel that carries blood that is low
in oxygen content from the body back to the heart.
The deoxygenated form of hemoglobin (deoxy-
hemoglobin) in venous blood makes it appear dark.
Veins are part of the afferent wing of the circulatory
system, which returns blood to the heart. In con-
trast, an artery is a vessel that carries blood that is
high in oxygen away from the heart to the body.