OBJECTIVE To evaluate acute changes in atrial and ventricular parameters by the use of cardiac magnetic resonance imaging (MRI) in patients with percutaneous transcatheter atrial septal defects (ASD) closure. METHODS The study included 14 patients (six males and eight females, 45 +/- 18 years) with congenital ASD. Cardiac MRI (1.5T Philips Intera CV) was performed before and within 24 hours after transcatheter ASD closure. Right atrial (RA) and left atrial (LA) dimensions, as well as right (RV) and left (LV) ventricular end-diastolic (ED) volumes were determined. Atrial size was assessed by planimetry of the maximum RA and LA areas in a standard four-chamber view, and ventricular volumes were calculated according to a modified Simpson's rule in short-axis views. RESULTS The mean RA decreased significantly from 27.6 +/- 6.4 cm(2) before closure to 24.4 +/- 5.6 cm(2) after the procedure (P = 0.0018), whereas the LA area did not change (24.1 +/- 4.7 cm(2) vs. 23.8 +/- 5.2 cm(2), P = 0.76). The RV volumes, volume index, and ejection fraction (EF) decreased significantly from 229 +/- 64 mL to 181 +/- 43 mL (P < 0.001, average reduction = 19% +/- 15%), from 126.0 +/- 37.2 mL/m(2) to 96.6 +/- 28.6 mL/m(2) (P < 0.0001) and from 64 +/- 5% to 58% +/- 7% (P = 0.01), respectively. The LV volumes and volume index remained unchanged (114 +/- 25 mL vs. 118 +/- 22 mL, P = 0.18, 63.5 +/- 13.5 mL/m(2) vs. 63.0 +/- 17.4 mL/m(2), P = 0.83). Left-right shunting decreased from 40% +/- 15% to 9% +/- 15% (P < 0.001). CONCLUSIONS Cardiac MRI can reveal detailed information on acute changes in shunt fraction and ventricular dimensions after ASD closure. ASD closure by percutaneous transcatheter device implantation results within 24 hours in a significant reduction of shunt fraction, RA and RV sizes, and RV function, whereas LA and LV dimensions remain unchanged.