To evaluate the occurrence of ECG abnormalities during fiberoptic bronchoscopy in relation to specific stages of the procedure and to hypoxemia, we prospectively studied 50 hospitalized patients aged 53 +/- 18 years (mean +/- SD) who were undergoing bronchoscopy by continuously monitoring cardiac rhythm with a continuous two-channel ECG recorder and oxygen saturation by using ear oximetry. Major disturbances of cardiac rhythm (ie, atrial, ventricular, or both) developed in 20 (40%) patients. Ventricular arrhythmias were recorded in ten patients (20%) and occurred with greatest frequency during passage of the bronchoscope through the vocal cords in five of these patients. Atrial arrhythmias were detected in 16 patients (32%), but their occurrence did not correlate closely with any one stage of the procedure. Arrhythmias were most frequent in association with periods of maximum oxygen desaturation in 12 of these 20 patients. Oxygen desaturation persisted for greater than one hour after bronchoscopy in 34 (68%) of 50 subjects. Notably, no correlation was observed between the frequency of arrhythmias during bronchoscopy and patients' age, sex, prior medications, or preexisting cardiac or pulmonary disorders. In no case was an ECG abnormality associated with adverse clinical sequelae.