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vaccination: A method of protecting the body against disease by injecting parts or all of a microorganism that will cause the body to develop antibodies against the microorganism and later fight off disease.

vacuum erection devices: Various manual or battery-operated pumps that a man can use to draw blood into the penis to create an erection.

vaginismus: Spasms of the muscles around the vaginal opening that prevent penile penetration.

valves: Structures consisting of leaflets that divide the chambers of the heart and prevent the backflow of blood from one chamber to another during contraction of the heart.

variant angina pectoris: Also called Prinzmetal's angina, these are attacks of chest pain caused by spasms of one or more coronary arteries almost always while a person is at rest.

vascular: Having to do with blood vessels and circulation.

vascular dementia: Dementia caused by narrowing or blockage of blood vessels in the brain or by a stroke or series of tiny strokes. Also called multi-infarct dementia.

vascular surgery: An operation to improve blood flow either by repairing leaks in blood vessels or by rerouting arteries to bypass blockages.

vasculitis: Inflammation of blood vessels.

vasectomy: An operation that ties off or cuts the tubes through which sperm travel from the testicles to the urethra; used as a form of birth control.

vasoconstrictor: A substance or condition, such as drugs, cold, fear, and nicotine, that causes blood vessels to narrow and thus de-creases the flow of blood.

vasodilation: A widening of the blood vessels that results in increased blood flow.

vasodilator: A substance or condition that causes blood vessels to open wider and increase the flow of blood.

vasospasm: Uncontrollable contraction or spasm of a blood vessel.

vector: An animal or insect that transmits an infectious disease from a reservoir to a susceptible host.

vein: A vessel that carries blood back to the heart.

venous: Pertaining to a vein.

venous leak: Seepage of blood out of a vein.

ventilator: Machine that inflates the lungs with oxygen.

ventricle: One of the two lower chambers of the heart. The right ventricle pumps blood to the lungs; the left ventricle pumps blood to the rest of the body.

ventricular arrhythmia: Abnormal heart rhythm that starts in the lower chambers of the heart; this rhythm disturbance can occur as a complication of a heart attack and impairs the heart's pumping ability.

ventricular fibrillation: A deadly heart rhythm in which the ventricles contract independently of the atria and in a chaotic manner.

ventricular myocardium: Heart muscle that makes up the lower chambers of the heart.

ventricular rupture: Break in the heart muscle that allows blood to escape into the pericardial sac.

ventricular septal defect: One or more holes in the septum, the muscular wall separating the right and left sides of the heart.

ventricular tachycardia: A very fast heartbeat that starts in the ventricles. Ventricular tachycardia can be deadly if it renders the heart unable to pump enough blood to the body.

venules: Small veins.

vertebra: One of the cylindrical bones that form the spine (plural: vertebrae).

vertebral artery: One of two blood vessels that run up the back of the neck and join at the base of the skull to form the basilar artery. The vertebral arteries carry blood from the heart to the brain.

vertebroplasty: A minimally invasive procedure to stabilize compressed vertebrae and alleviate pain. A needle is inserted into the compressed portion of a vertebra and surgical cement is injected to support the vertebra and prevent further collapse.

vertigo: Dizziness; often a spinning sensation or a feeling that the ground is tilting.

very low-calorie diet: A weight-loss diet that allows 800 or fewer calories per day (usually followed under medical supervision).

very-low-density lipoprotein: A lipoprotein that transports triglyceride manufactured in the liver to fat tissue in the body. VLDL eventually becomes low-density lipoprotein (LDL) after the triglyceride has been removed.

vestibular system: The balance organs, located in the labyrinth in the inner ear.

viral: Pertaining to or caused by a virus.

virtues: Core characteristics that are universally valued by philosophers and religions across time and cultures, such as wisdom and courage.

virulent: A disease or condition that is highly infectious or dangerous or rapidly progressing.

viscera: The internal organs, especially those found in the abdomen.

visceral fat: Fat that lies beneath the abdominal wall, in the spaces surrounding the liver, intestines, and other organs. Sometimes called belly fat or abdominal adiposity.

visual acuity: The eye's ability to see sharply, usually measured in comparison to what a normal eye would see from 20 feet. Problems in visual acuity can usually be corrected with eyeglasses.

visual cortex: The part of the occipital lobe in the brain that processes visual stimuli.

visual field: The full scope of what the eye sees; includes central and peripheral vision.

visualized laser-assisted prostatectomy: A technique used to treat benign prostatic hyperplasia (enlarged prostate gland) that allows the surgeon to view the prostate directly while it is being shrunk by a laser beam.

vital signs: Measurements that indicate how well the body is functioning, including pulse rate, respiration (breathing rate), temperature, and blood pressure.

vitamin D: A hormone that plays a key role in ensuring the absorption of calcium from the intestines.

vitrectomy: A microsurgical procedure in which part of the vitreous humor of the eye is removed and then replaced with sterile saline or some other fluid.

vitreous humor: The clear, gel-like substance that fills the space behind the lens of the eye and supports the shape of the rear portion of the eye.

VLDL: Abbreviation for very-low-density lipoprotein, a lipoprotein that transports triglyceride manufactured in the liver to fat tissue in the body. VLDL eventually becomes low-density lipoprotein (LDL) after the triglyceride has been removed.

VO2 max: The body's maximum capacity for oxygen consumption during peak exertion. Also known as aerobic power, maximal oxygen consumption, or cardiorespiratory endurance capacity.

volatile oils: Unstable components of a preparation that evaporate easily.

VSD: Abbreviation for ventricular septal defect—one or more holes in the septum, the muscular wall separating the right and left sides of the heart.

vulnerary: An agent that is believed to aid in wound healing.

vulvar vestibulitis: Inflammation of the tissue around the opening of the vagina that makes sexual activity painful.

vulvodynia: Pain in the vulva that may or may not be brought on by touch or pressure.