text: Use of Cardiopulmonary Stress Testing for Patients With Unexplained Dyspnea Post Coronavirus Disease The authors used cardiopulmonary exercise testing CPET to define unexplained dyspnea in patients with post acute sequelae of severe acute respiratory syndrome coronavirus 2 SARS CoV 2 infection PASC We assessed participants for criteria to diagnose myalgic encephalomyelitis chronic fatigue syndrome ME CFS Approximately 20 of patients who recover from coronavirus disease COVID remain symptomatic This syndrome is named PASC Its etiology is unclear Dyspnea is a frequent symptom The authors performed CPET and symptom assessment for ME CFS in 41 patients with PASC 8 9 3 3 months after COVID All patients had normal pulmonary function tests chest X ray and chest computed tomography scans Peak oxygen consumption peak VO sub 2 sub slope of minute ventilation to CO sub 2 sub production VE VCO sub 2 sub slope and end tidal pressure of CO sub 2 sub PetCO sub 2 sub were measured Ventilatory patterns were reviewed with dysfunctional breathing defined as rapid erratic breathing Eighteen men and 23 women average age 45 13 years were studied Left ventricular ejection fraction was 59 9 Peak VO sub 2 sub averaged 20 3 7 mL kg min 77 21 predicted VO sub 2 sub VE VCO sub 2 sub slope was 30 7 PetCO sub 2 sub at rest was 33 5 4 5 mm Hg Twenty four patients 58 5 had a peak VO sub 2 sub 80 predicted All patients with peak VO sub 2 sub 80 had a circulatory limitation to exercise Fifteen of 17 patients with normal peak VO sub 2 sub had ventilatory abnormalities including peak respiratory rate 55 n 3 or dysfunctional breathing n 12 For the whole cohort 88 of patients n 36 had ventilatory abnormalities with dysfunctional breathing n 26 increased VE VCO sub 2 sub n 17 and or hypocapnia PetCO sub 2 sub 35 n 25 Nineteen patients 46 met criteria for ME CFS Circulatory impairment abnormal ventilatory pattern and ME CFS are common in patients with PASC The dysfunctional breathing resting hypocapnia and ME CFS may contribute to symptoms CPET is a valuable tool to assess these patients 