To investigate the relationship between left atrial function and secretion of atrial natriuretic peptide (ANP), we analyzed left ventricular inflow and pulmonary venous flow, left atrial dynamics, intracardiac pressures, and plasma ANP level in 92 patients with various cardiac diseases. From the apical four-chamber view, maximal left atrial volume and percent fractional change of the left atrial area during atrial systole (LA-%AC) were calculated. The ratio of peak early filling velocity to peak atrial systolic velocity (E/A) in the left ventricular inflow and the ratio of peak systolic velocity to peak diastolic velocity (S/D) in the pulmonary venous flow were measured with the pulsed Doppler method. A significant linear correlation was found between plasma ANP levels and pulmonary capillary wedge pressure. Significant linear correlations were also found between left ventricular end-diastolic pressure and both maximal left atrial volume and LA-%AC. Plasma ANP level was significantly correlated with maximal left atrial volume, LA-%AC, E/A, and S/D. A multivariate analysis revealed that only LA-%AC was significantly correlated with the plasma ANP level. These results suggest that left atrial systolic dysfunction associated with a left atrial afterload mismatch is closely related to the ANP secretion.