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We thank Oldham et al. 1 for their excellent study on low ventricular filling pressures as a cause of exercise intolerance and dyspnea. Although only 5 patients in this cohort had a tilt table test positive for postural tachycardia syndrome (POTS) and only 2 had autonomic neuropathy, we suspect that these findings are applicable to the majority of patients with POTS. POTS arises from multiple etiologies, but the hallmark features of exercise intolerance, orthostatic tachycardia, fatigue, dizziness, and, in many cases, dyspnea upon exertion or at rest are common to all patients, regardless of the underlying cause. Most patients undergo extensive noninvasive cardiac testing and are often told that their symptoms are secondary to deconditioning, given a common finding of poor exercise tolerance on an exercise stress test. Previously, a low stroke volume and decreased cardiac mass in patients with POTS have been …