While echocardiography has been used to noninvasively document indirect effects on the heart of left-to-right shunting through a patent ductus arteriosus, no noninvasive technique has been developed to image the duct itself. In this study, 35 sequential studies were performed on 28 patients with a mechanical sector scanner to image the distal pulmonary artery and its bifurcation by scanning along the axis of the right ventricular outflow tract. Cross-sectional imaging, just superior to the take-off of the right pulmonary artery, provided visualization of the patent ductus as a distal continuation of the pulmonary artery connecting to the descending aorta. Ductal visualization by cross-sectional echo was validated by saline echo contrast observations of right-to-left and left-to-right shunting through the duct in 14 patients, by surgical observations in 11, angiographic observations in 13 and autopsy observations in three. Angiographic size of the ductus arteriosus, whether constricted or widely patent, tortuous or straight, was predicted correctly and echo/angiographic correlations for smallest inner ductal dimension were excellent (r = 0.97). This study provides a method for and validates the direct imaging of the ductus arteriosus and suggests that cross-sectional echocardiography can accurately predict ductal contour and quantitative ductal cross-sectional size noninvasively.