A 43-yr-old woman developed severe exertional dyspnea after an unsuccessful attempt to correct a total right anomalous pulmonary venous connection. A clotted anastomosis resulted in unilateral pulmonary venous obstruction. Investigation excluded airway diseases, left ventricular failure, and severe pulmonary hypertension as the cause of dyspnea. Exercise studies demonstrated a markedly abnormal ventilatory pattern consistent with excess vagal stimuli to the respiratory center. Temporary and then permanent vagal interruption markedly altered the respiratory pattern and improved her functional status from New York Heart Association Class III to Class I, confirming that vagal afferents were the cause of the dyspnea.