Transesophageal two-dimensional (2-D) echocardiography (TEE: horizontal sector scan) combined with the pulsed Doppler method was performed to determine the size of atrial septal defect (ASD) and to measure directly shunt flow signals through the defects in six ASD patients (32 +/- 16 yrs) confirmed by cardiac catheterization. The size of the defect in the horizontal dimension was measured by TEE; the vertical dimension of the defect was determined from the distance of the transesophageal probe positions of the rostral and caudal margins of the defect. The size of defect determined by TEE was compared with that observed at surgery. Shunt flow signals were recorded by the pulsed Doppler technique by setting the sample volume at the center of the defect. Left-to-right shunt flow was determined as follows: shunt flow volume (ml/min) = mean velocity (cm/s) x the area of a defect (cm2) x 60. The shunt flow was compared with that obtained by the Fick's method. In all patients, TEE accomplished unequivocal visualization of a defect. The defect sizes by TEE correlated well with measurements obtained at surgery (r = 0.66). A clear laminar shunt flow with its peak in late systole and atrial systole was observed. Significant correlations were obtained between shunt volumes by TEE and those by the Fick's method (r = 0.91, p less than 0.05). Thus, TEE proved a useful method for diagnosing ASD and for evaluating shunt flow volumes.