Two-dimensional and Doppler echocardiographic methods are used to noninvasively detect atrial septal defects. The value of these methods to predict the magnitude of intracardiac left-to-right shunts has not been thoroughly investigated. In this study, we derived right ventricular (RV) and septal defect dimensions, and Qp/Qs-ratios from two-dimensional and Doppler echocardiography in 30 consecutive patients (17 females, 3 males, age 37 +/- 17 years) with invasively confirmed atrial septal defects. Noninvasively obtained parameters were compared to atrial shunt size as measured by oxymetry. RV dimensions correlated only poorly (RV length: r = 0.53, p < 0.005; RV-diameter r = 0.45 p < 0.05), but septal defect dimensions (r = 0.67, p < 0.001) and Qp/Qs-index (r = 0.65, p < 0.05) correlated fairly with shunt size. RV dilatation was highly sensitive (100%) but only moderately specific (67%) as an indicator of shunts > 30%. A defect length > or = 15 mm was moderately sensitive (81%) but highly specific (100%) and a Qp/Qs-index > or = 1.45 was highly sensitive (100%) and specific (76%) to detect shunts > 30%. None of the noninvasive parameters investigated in this study was able to differentiate moderate (> 30% but < 50%) from large ( > or = 50%) intracardiac left-to-right shunts.