A patient underwent exercise testing during evaluation for unexplained dyspnea. Evidence of ventilation-perfusion mismatch was noted and subsequent testing revealed multiple pulmonary emboli. Ventilation perfusion parameters by serial exercise testing progressively improved during the course of the patient's illness but did not totally normalize. A discussion of the utility of exercise testing in the evaluation of the patient with unexplained dyspnea is provided and the potential value of serial exercise testing in the management of patients with pulmonary emboli is discussed.