Tachycardia is the fast beating of the heart. In adults, it refers to heart rates higher than 100 beats per minute. Tachycardia may be a normal physiological response to stress, but depending on the cause and how healthy the patient is, tachycardia could be harmful and need medical treatment. In some cases, tachycardia can cause death.
Tachycardia can be harmful in two ways. First, when the heart beats too rapidly, it may perform inefficiently. Second, the faster the heart beats, the more oxygen and nutrients the heart requires. This can be especially problematic for patients suffering from ischaemic heart disease.