We compared 8 patients with COPD and fixed atrial fibrillation (group I) and 46 patients with COPD and sinus rhythm in ecg (group II). None of the patients had valvular heart disease, arterial hypertension or clinical signs of coronary artery disease. The studied groups did not differ while comparing their gas measurements, spirometry, pulmonary hypertension and right ventricular diameter (as measured in echo study). Patients with fixed atrial fibrillation had larger circuit and area of right atrium (p = 0.001), left atrial and left ventricular diameter (p = 0.001) as well as lower LV function (expressed by FS%). In conclusion, enlargement of both atria may be considered as a cause for fixed atrial fibrillation in patients with COPD. However symptomless coronary artery disease rather then COPD may be the reason for this arrhythmia.