tachycardia A rapid heart beat. This happens as a normal response to physical work and exercise, up to a maximum of about 200 beats per minute in a young adult, decreasing with age to about 150 at age 70. This is sinus tachycardia and it is brought about by the increased discharge rate of the heart's built-in pacemaker, the sino–atrial node, under the influence of the sympathetic nervous system. Likewise heart rate increases in response to excitement or anxiety or to blood loss. Paroxysmal tachycardia — disturbing attacks of palpitation — can occur for no apparent reason and often with no evidence of cardiac abnormality. Ventricular tachycardia is more ominous: driven from an abnormal focus of electrical activity in the ventricles themselves.

Stuart Judge

tachycardia (tak-i-kar-diă) n. an increase in the heart rate above normal. sinus t. tachycardia that may occur normally with exercise or excitement. It may also be due to illness, such as fever. supraventricular t. (SVT) tachycardia usually due to an accessory conduction pathway between the atria and ventricles (see Wolff-Parkinson-White syndrome) but sometimes stemming from an abnormal area in the atria. ventricular t. (VT) tachycardia stemming from an abnormal focus of electrical activity in the ventricles, which can result in a sudden drop in blood pressure or cardiac arrest. See also paroxysmal tachycardia.

tachycardia An increase in heart rate. The heart rate is controlled by the opposing actions of the sympathetic nervous system, which accelerates the heartbeat; and the parasympathetic nervous system, which slows it down. The heart rate is normally approximately 70 beats per minute. During exercise there is an increase in sympathetic activity and tachycardia occurs: the heart rate increases to up to 110 beats per minute. Immediately after exercise, at rest, the heart rate decreases to around 60 beats per minute (bradycardia), due to an increase in parasympathetic activity.

tachycardia Rapid heartbeat, as occurs after exercise; may also occur, without undue exertion, as a result of anxiety, and in anaemia and vitamin B1 deficiency.

tach·y·car·di·a / ˌtakiˈkärdēə/ • n. an abnormally rapid heart rate.