OBJECTIVES: The purpose of this study was to prospectively characterize the reduction in right atrial (RA) area and right ventricular (RV) volume after transcatheter closure of atrial septal defect (ASD) and to investigate factors that may predict magnitude of resolution in right heart enlargement. BACKGROUND: Secundum ASD can cause volume overload of the right side of the heart with the potential for development of late complications. Little is known about reduction in right heart size after closure of ASD. METHODS: Transthoracic echocardiography was performed in 38 patients undergoing transcatheter closure of ASD. The RA area and RV volume were measured prior (n = 38), within 24 hours (n = 37), at 3 to 6 months (n = 24), at 12 months (n = 20) and at 24 months (n = 10) after closure of ASD. Change over time within the study group was assessed and the study group was compared to a control group of 19 patients with structurally normal hearts. RESULTS: Indexed RA area decreased from baseline to 3- to 6-month follow-up (p = 0.004) as did indexed RV volume (p < 0.0001). Indexed RV volume was similar to that in the control group at 24 months (p = 0.3); however, indexed RA area remained greater than in the control group (p = 0.006). Decrease in indexed RA area over the first 12 months of follow-up was related to young age at time of closure by regression analysis (r = 0.55, p = 0.013). CONCLUSION: Closure of secundum ASD results in decreased indexed RV volume comparable to that in control subjects at 24 months following closure. Indexed RA area remains increased compared to that in control subjects but does decrease over time. Decrease in RA area is inversely proportional to age at time of ASD closure. Long-term follow-up is required to evaluate the clinical impact of persistently increased RA size.