Abslract Bronchoscopy, as an endoscopic technique, is associated with respiratory and circulatory disorders. Cardiac rhythm disorders are the most common cardiovascular complications of bronchoscopy. In order to study ECG changes during bronchological procedures, ECG monitoring was undertaken (30 min before, during and 30 min after bronchoscopy) in 100 patients, 76 with bronchial carcinoma and 24 suffering from some other pulmonary disease. Within the same intervals PaO2, PaCO2 and pH were recorded. All recorded arrhythmias were classified as minor and major. According to arrythmia noted during bronchoscopy, patients were divided into two groups: group 1 comprised 70 patients without arrythmia or with minor arrythmia (70%) and group 2, 30 patients with major arrythmia (30%). No significant difference was noted in associated cardiac disease, cardiological medication, blood pressure, pulse rate, PaO2, P, CO2 and pH (P<0.05). The only statistically significant difference between the two groups of patients was related to localization of tumour in the lungs. We could not correlate the occurrence of major arrythmia during bronchoscopy in patients with lung carcinoma with any underlying cardiopulmonary condition. Significant differences wre noted in effects of turnout localization, i.e. major arrhythmias are more common and more dangerous in cases of tumours of the left bronchial trunk (possible bronchoscopic stimulation of the left stellate ganglion), and we therefore believe that ECG monitoring is desirable in these cases for the early detection and appropriate management of haemodynamically dangerous arrhythmias.