Background: Isolated atrial fibrillation (AF) represents a unique subset of the AF in which known risk factors and cardiovascular diseases are not present. Objective: The objective of this study was to determine whether there are changes in interatrial conduction, measured non-invasively with electrocardiogram (ECG) and with ultrasound, in patients with isolated AF. Subjects and Methods: 83 patients with isolated FA and 80 healthy controls were included in the study. P-wave on the surface ECG and length of atrial electromechanical conduction time (EMT) were recorded. EMT is measured as the time interval from the start of the P-wave on the ECG to the peak late diastolic wave of the septal and lateral mitral annulus (EMT-S and EMT-L) and tricuspid annulus (EMT-T) using tissue Doppler echocardiography. Results: Patients with isolated atrial fibrillation had significant morphological changes in the appearance of P-wave (86.8% vrs.13.8%), prolonged duration of P-wave (115 ms vrs. 98.5 ms) and significantly prolonged duration of atrial electromechanical conduction time (EMT), especially EMT-L (EMT-L 129 ms vrs. 99 ms), compared to a healthy control population. Conclusion: LA EMT was significantly prolonged and P-wave morphology changed in patients with isolated FA in comparison to the healthy population, suggesting an impaired atrial conduction. Key words: atrial fibrillation, interatrial conduction, interatrial block, electromechanical conduction time, electrocardiography, echocardiography, tissue Doppler echocardiography.