AIMS: Chronic atrial fibrillation causes mechanical remodelling of the atria, but it is uncertain whether self-terminating episodes of paroxysmal atrial fibrillation (PAF) alter atrial mechanical function during normal sinus rhythm. This study was designed to assess the relationship between the frequency of symptomatic arrhythmic episodes and pulmonary venous flow (PVF) pattern among patients with PAF. METHODS AND RESULTS: The effect of symptomatic arrhythmic episodes on PVF was studied in 85 patients with lone PAF (age 48+/-8 years, 66 men). PVF was measured with transthoracic echocardiography during sinus rhythm. Adequate recordings of PVF were achieved in 81 (95%) patients. Peak systolic PVF had an inverse correlation (r=-0.35, P=0.002) with the frequency of PAF episodes. The peak systolic PVF was 76+/-14 cm/s vs 62+/-12 cm/s (P=0.008) among the quartiles with the most and the least frequent episodes of PAF, respectively. There were no significant differences in the other echocardiographic measurements or demographic variables. CONCLUSIONS: Frequent arrhythmic episodes significantly diminished systolic PVF among patients with PAF, suggesting that PAF results in gradual mechanical remodelling of the atrium, which may favour recurrence and perpetuation of AF and/or formation of atrial thrombus.