Doppler echocardiography enables the possibility of determining pulmonary to systemic flow ratios in patients with left to right shunts. Volume flow is calculated as the product of mean velocity over time, as evaluated by pulsed Doppler, and the cross-sectional area through which the flow passes. Appropriate sites for measurement of velocity and cross-sectional area of flow are the ascending aorta, right ventricular outflow tract and pulmonary artery as well as the tricuspid and mitral valve orifices. Velocity is always recorded as parallel as possible to the direction of flow. Echocardiographic measurements of the area of flow are carried out at the level of the sample volume. In the presence of an atrial or ventricular septal defect, the flow in the ascending aorta normally serves as systemic flow; alternatively, mitral or tricuspid flow may be used to cross-check these values. The latter serves for calculation of systemic flow in patent ductus arteriosus. In atrial or ventricular septal defect, the pulmonary flow is normally derived in the region of the pulmonary artery; in patent ductus arteriosus, however, in the region of the ascending aorta. As an alternative, or for confirmative use, in atrial septal defect the tricuspid flow and in ventricular septal defect and patent ductus arteriosus the mitral flow, can be taken into consideration. Studies we performed in 31 patients with atrial septal defect showed a close correlation between Doppler echocardiographic measurements and data obtained by cardiac catheterization and radionuclide studies.(ABSTRACT TRUNCATED AT 250 WORDS)