OBJECTIVE Mechanisms underlying lone atrial fibrillation (LAF) are poorly defined. We sought to investigate indices of left atrial (LA) function in patients with recurrent LAF, in comparison with that in healthy subjects. RESULTS Investigations were performed in 42 patients aged 51.8 +/- 8.7 at least 30 days after the last episode of LAF and in 38 healthy controls. Each subject underwent echocardiographic evaluation including left ventricular parameters and LA function indices. LA ejection fraction served as a measure of LA systolic performance, and acceleration (SAT) and deceleration time (SDT) of systolic phase of pulmonary venous flow (PVF) corresponded to LA relaxation and compliance, respectively. Patients with LAF showed significantly lower values of SAT (179.1 +/- 63.2 vs. 199.2 +/- 45.1 ms, P < 0.02) and higher values of SDT (250.8 +/- 81.6 vs. 211.7 +/- 57.3 ms, P < 0.01) when compared with controls. No significant differences were found with respect to other measured parameters. The combination of SAT < 185 ms and SDT > 239 ms showed a positive predictive value of 92% in the identification of patients prone to LAF. CONCLUSIONS This study suggests that (i) patients with LAF have abnormalities of the systolic phase of PVF and (ii) Doppler estimation of PVF seems to be very valuable in the evaluation of patients with LAF.