vagus nerve The major nerve of the parasympathetic nervous system that slows the heart rate when stimulated. It is involved in gastrointestinal function.
valvotomy/valvulotomyAn open-heart operation to correct a blocked heart valve. A newer, less invasive technique known as balloon valvulotomy employs a balloon-tipped catheter to open up the valve.
valvuloplasty Reconstructive open-heart surgery to repair a defective heart valve. Balloon valvuloplasty uses a balloon-tipped catheter. When inflated, the balloon can separate any narrowed or stiffened leaflets of the valve.
varicose veins Swollen, twisted veins found mostly in the legs. They swell because blood drains back down into the legs and pools, the result of defective valves in the veins.
vasoconstriction Constriction of the blood vessels.
vasodilator A substance that causes blood vessels to relax or dilate.
vasospasmSpasm (an abnormal, sudden, and involuntary contraction) of the blood vessels.
vasovagal response Temporary light-headedness or loss of consciousness because of a sudden reduction in heartbeat and blood pressure. People who faint at the sight of blood typically have an extreme vasovagal response.
vein A blood vessel that conveys blood from various parts of the body back to the heart.
venous thrombosis The medical term for blood clots in the veins.
ventricles The two lower or main pumping chambers of the heart. They receive blood from the atria and pump it to the lungs and the various parts of the body .
ventricular fibrillationRapid, uncoordinated, and ineffective contractions of the heart initiated by electrical impulses from the ventricles. Can be fatal if it is not reversed.
VEST scan One of the newest radionuclide diagnostic tests; it uses a miniaturized radionuclide detector (VEST) that can be worn for ambulatory monitoring.