Traditionally, any heart rate greater than 100 beats per minute is classified as a tachycardia. Tachycardia can frequently be a normal finding; young adults can have heart rates of 150–180 beats per minute at peak exercise due to sympathetic activation. However, tachycardia can be an abnormal finding associated with hemodynamic collapse. Tachycardias are usually classified by their QRS morphology/duration: normal or wide complex. If the QRS complex has a normal duration and morphology, the ventricles are being activated normally and a tachycardia site within the ventricle is excluded. For this reason narrow QRS complex tachycardias are frequently called supraventricular tachycardias.