[4] Some causes of tachycardia include:[5] Drug related: The upper threshold of a normal human resting heart rate is based on age.

Fever, hyperventilation, diarrhea and severe infections can also cause tachycardia, primarily due to increase in metabolic demands.

This energy shortage in muscle cells causes an inappropriate rapid heart rate in response to exercise.

[12][13] Those with GSD-V also experience "second wind", after approximately 6–10 minutes of light-moderate aerobic activity, such as walking without an incline, where the heart rate drops and symptoms of exercise intolerance improve.

[12][13][14] An increase in sympathetic nervous system stimulation causes the heart rate to increase, both by the direct action of sympathetic nerve fibers on the heart and by causing the endocrine system to release hormones such as epinephrine (adrenaline), which have a similar effect.

Certain endocrine disorders such as pheochromocytoma can also cause epinephrine release and can result in tachycardia independent of nervous system stimulation.

[15] The upper limit of normal rate for sinus tachycardia is thought to be 220 bpm minus age.

Other causes may include autonomic nervous system deficits, autoimmune response, or drug interactions.

[17] Ventricular tachycardia (VT or V-tach) is a potentially life-threatening cardiac arrhythmia that originates in the ventricles.

[18] Both of these rhythms normally last for only a few seconds to minutes (paroxysmal tachycardia), but if VT persists it is extremely dangerous, often leading to ventricular fibrillation.

AVRT may involve orthodromic conduction (where the impulse travels down the AV node to the ventricles and back up to the atria through the accessory pathway) or antidromic conduction (which the impulse travels down the accessory pathway and back up to the atria through the AV node).

Most antiarrhythmics are contraindicated in the emergency treatment of AVRT, because they may paradoxically increase conduction across the accessory pathway.

[10] Stable means that there is a tachycardia, but it does not seem an immediate threat for the patient's health, but only a symptom of an unknown disease, or a reaction that is not very dangerous in that moment.

[10] The word tachycardia came to English from Neo-Latin as a neoclassical compound built from the combining forms tachy- + -cardia, which are from the Greek ταχύς tachys, "quick, rapid" and καρδία, kardia, "heart".

As a matter both of usage choices in the medical literature and of idiom in natural language, the words tachycardia and tachyarrhythmia are usually used interchangeably, or loosely enough that precise differentiation is not explicit.

[28] But the prescription will probably never be successfully imposed on general usage, not only because much of the existing medical literature ignores it even when the words stand alone but also because the terms for specific types of arrhythmia (standard collocations of adjectives and noun) are deeply established idiomatically with the tachycardia version as the more commonly used version.

But the power to differentiate in an idiomatic way is not lost, regardless, because when the specification of physiologic tachycardia is needed, that phrase aptly conveys it.