As awareness of postural tachycardia syndrome (POTS) has increased in recent years,1-3 our laboratory has received numerous patient referrals for “POTS going to faint.” These comprise patients who, during tilt table testing, have development of excessive tachycardia, sometimes gradually decreasing blood pressure and symptoms of orthostatic intolerance, followed by a simple postural faint (current designation “reflex neurocardiogenic syncope”4). Consider 2 representative teenage patients placed on a tilt table for a 20- to 30-minute supine equilibration period and then tilted upright to 70 degrees. Both have development of excessive increases in heart rate within 5 minutes of the onset of upright tilt (Figure 1). Both become lightheaded and nauseated and have development of progressive neurocognitive impairment. Respirations deepen, and end tidal carbon dioxide is significantly decreased. They are both pale and somewhat diaphoretic. Blood pressure may slowly decrease. Just before pronouncing the diagnosis of POTS, 1 patient abruptly loses consciousness in association with a rapid decrease in blood pressure and heart rate characteristic of the “vasovagal faint” variant of reflex syncope because of the decrease in blood pressure (the vaso or vascular part) followed immediately by a sudden drop in heart rate (the vagal part).5 This causes an equally abrupt change in the diagnosis from POTS to simple faint. The other patient continues to have an excessively increased heart rate and symptoms of orthostatic intolerance but has no decrease in blood pressure or heart rate, or loss of consciousness. Blood pressure and heart rate data for the representative tilt subjects are shown in Figure 1. These scenarios have fostered concerns about the clinical and physiological similarities and differences between simple faint and POTS. The answer appears to be a qualified no to clinical similarity and a qualified yes to physiological similarity. One could easily reverse this question and ask whether there are clinical and physiological differences between simple faint and POTS. The answer appears to be a qualified yes to clinical difference and a qualified no to physiological difference. The most notable differences between POTS and simple fainting are found in their clinical presentations, and therefore history taking is paramount in diagnoses. POTS is a chronic day-to-day form of orthostatic intolerance, and simple faint is most often episodic and associated with long periods of “wellness.” Figure 1 The figure shows heart rate in the top panel and mean arterial pressure in the bottom panel during upright tilt to 70 degrees. A representative patient with POTS is shown in red and a representative patient with syncope is shown in green. Excessive tachycardia ...