an increase in the frequency of cardiac contractions. In some cases it is not perceived subjectively; in others, it is accompanied by palpitations.

A distinction is made between sinus tachycardia, or the accelerated generation of impulses in the sinus node of the heart, and paroxysmal tachycardia. Sinus tachycardia, manifested by contractions generally ranging between 90 and 120 per minute, may be caused by such physiological factors as increased environmental temperature, physical and mental tension, or the ingestion of food. Sinus tachycardia may also be caused by such pathological states as fever, anemia, diffuse toxic goiter, heart failure, and neurasthenia. Nervous and humoral influences on the heart, such as adrenalin and thyroxine, are important contributing factors in the genesis of sinus tachycardia. The accelerated rhythm of cardiac contractions may have an unfavorable effect on metabolism in the myocardium and on blood circulation. When tachycardia is a symptom of disease, the underlying disease is treated.