ObjectivePatients with recurrent chest pain but no evidence of coronary artery disease often meet diagnostic criteria for panic disorder (PD). However, it can be argued that the phenomenological diagnosis of PD may not be valid in these normal coronary chest pain (NCCP) patients. The purpose of this study is to additionally validate the diagnosis of PD in chest pain patients by comparing PCO2levels before and during myocardial stress scintigraphy in those with and without PD.MethodEnd-tidal PCO2was measured before and during myocardial stress scintigraphy in 22 patients being evaluated for chest pain. Psychiatric diagnoses were assessed by structured interview.ResultsEleven of the 19 patients (58%) with negative scintigrams met DSM-III-R diagnostic criteria for current panic disorder. Prestress PCO2levels were significantly lower in these patients. Eight of the nine NCCP patients with prestress PCO2< 34 mm Hg had PD.ConclusionsThe finding of stress-related hypocapnia associated with PD in NCCP patients provides additional support for the validity of the diagnosis of PD in this population. The potential value of PCO2measurements in screening for PD in patients with chest pain merits additional study.