Tachycardia

n. rapid heart rate (Medicine)

Tachycardia is a form of cardiac arrhythmia which refers to a rapid beating of the heart. By convention the term refers to heart rates greater than 100 beats per minute in the adult patient. Tachycardia may be a perfectly normal physiological response to stress. However, depending on the mechanism of the tachycardia and the health status of the patient, tachycardia may be harmful, and require medical treatment. In extreme cases, tachycardia can be life threatening.
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Tachycardia /tachy·car·dia/ abnormally rapid heart rate.tachycar´diac atrial tachycardia a rapid cardiac rate, usually 160–190 per minute, [more]Tachycardia - Community and Resources

Noun
1. abnormally rapid heartbeat (over 100 beats per minute)
(hypernym) cardiac arrhythmia, arrhythmia

A rapid heart rate, usually defined as greater than 100 beats per minute.