Transcatheter closure of a secundum defect using a septal occluder is a safe and effective procedure based on long-term follow-up, but no clinical studies have examined immediate hemodynamic changes. We evaluated pulmonary venous flow velocity pattern before and immediately after deployment of the Amplatzer septal occluder for closure of atrial septal defect. From May 2003 to January 2005, 48 patients with secundum atrial septal defect received transcatheter closure with complete occlusion. Patients were divided into two groups according to age: pediatric group, under 16 years (n = 30, age 7.3 +/- 3.2 years), and adult group, 16 years or older (n = 18, age 30.1 +/- 11.4 years). Pulmonary venous flow pattern was recorded by transesophageal echocardiography before and immediately after occluder deployment. Immediately after deployment in both patient groups, pulmonary vein systolic (S) and diastolic (D) wave velocity decreased, but atrial reversal (AR) wave velocity increased. In the pediatric group, S-wave was 56.1 +/- 17.1 versus 35.5 +/- 11.3 cm/sec (P < 0.001); D-wave was 57.6 +/- 12.5 versus 42.9 +/- 11.8 cm/sec (P < 0.001); and AR wave velocity was 12.2 +/- 3.8 versus 15.5 +/- 4.1 cm/sec (P < 0.001). In the adult group, S-wave was 48.4 +/- 13.7 versus 32.7 +/- 10.3 cm/sec (P < 0.001); D-wave was 51.9 +/- 11.7 versus 38.0 +/- 8.5 m/sec (P < 0.001); and AR wave velocity was 12.1 +/- 4.1 versus 16.2 +/- 4.9 cm/sec (P < 0.001). Comparison of pulmonary venous flow before and immediately after deployment of the Amplatzer septal occluder provides an excellent model to evaluate the influence of an atrial communication on pulmonary venous flow. Pulmonary venous forward flow decreases following atrial septal defect (ASD) closure.