Information regarding the relation of left atrial (LA) function to transmitral and pulmonary venous (PV) flow is limited. Using transesophageal echocardiography, we analyzed this relation in 23 patients with dilated cardiomyopathy (DCM) and 25 patients with hypertrophic cardiomyopathy (HCM). Left atrial appendage (LAA) function was assessed as a substitute for overall LA function. Transmitral and PV flow-velocity variables, the LAA emptying flow velocity (LAA-A), and the LAA ejection fraction (LAA-EF) were determined. Each patient group was divided into two subgroups with a normal (<15 mm Hg) or elevated (≥15 mm Hg) mean pulmonary wedge pressure (PWP). Transmitral and PV flow patterns as well as LA function were similar in the two subgroups with a normal PWP (11 patients with DCM and 14 patients with HCM). For the subgroups with an elevated PWP, however, the peak velocity ratio of the early filling wave (E) to atrial contraction wave (A) was higher in DCM patients (n = 12) than in HCM patients (n = 11) (2.1 ± 0.7 vs 1.3 ± 0.2; p < 0.01). This difference mostly resulted from a lower A velocity in the DCM group than in the HCM group (30 ± 10 cm/sec vs 43 ± 7 cm/sec; p < 0.05). In addition, the reverse flow velocity at atrial contraction in the PV was lower in the DCM group than in the HCM group (19 ± 8 cm/sec vs 37 ± 8 cm/sec; p< 0.01). These findings were associated with poorer LA systolic function in the DCM group (LAA-A, 35 ± 13 cm/sec vs 60 ± 11 cm/sec; LAA-EF, 37% ± 12% vs 55% ± 15%, p < 0.05, respectively). Our data suggest that a restrictive transmital flow pattern develops more easily in DCM than in HCM because LA dysfunction is present in DCM, and that LA contractility plays an important role in determining the atrial contraction wave of transmitral and PV flows with elevated LA pressure.