The electrocardiogram was monitored in 51 patients during fiberoptic bronchoscopic procedures and was compared to recordings made before premedication. Sixteen of the patients had heart disease. During the bronchoscopic procedure, the heart rate increased by 154 "/- 5 percent (+/- SE). The frequency of atrial ectopic beats was minimally increased, by an average 0.15 +/- 0.12 beats per minute (not significant). Ventricular ectopic beats became less frequent during the bronchoscopic procedure (-0.17 +/- 0.41 beats per minute; not significant), and there was no ventricular tachycardia. Frequent ventricular ectopic beats were seen mainly during bronchoscopic procedures in patients with coronary heart disease, but even in this group, ventricular ectopic beats became less frequent than at rest (-1.13 +/- 1.46 beats per minute; not significant). The nearly uniform sinus tachycardia that was observed was well tolerated but could predispose coronary patients to ischemia; however, the fiberoptic bronchoscopic procedure per se does not enhance prior ectopy.