Cardiac rhythm was monitored in 70 patients prior to, during, and following fiberoptic bronchoscopic procedures. Minor abnormalities in rhythm were frequent. Major cardiac arrhythmias occurred in 11% (8/70) of the patients during the bronchoscopic procedure. All arrhythmias were self-limited and had no hemodynamic consequence. Patients with evidence of coronary arterial disease, chronic obstructive pulmonary disease, or previously known premature ventricular contractions were at no higher risk for developing major arrhythmias. Hypoxemia (arterial oxygen pressure less than 60 mm Hg) at the end of the procedure correlated significantly with the development of new major arrhythmias.