BACKGROUND--Shunt vessels were imaged and shunt flow was analysed by cross sectional and Doppler echocardiography in 12 patients who had had 14 shunt procedures (nine left Blalock-Taussig shunts, three right Blalock-Taussig shunts, one modified Waterston shunt, and one central shunt). METHODS--The shunt vessels were classified by echocardiography as uniformly patent, segmentally stenosed, and uniformly stenosed. These findings were compared with those of angiography. Also the peak flow velocities at the aortic and the pulmonary ends of the shunt vessels were measured by Doppler echocardiography and the ratio of these values was calculated for each shunt. RESULTS--Twelve (85.7%) of 14 shunt vessels were imaged along their entire length by cross sectional echocardiography. The two remaining shunt vessels were only partially imaged. In 10 patients who also had angiography the echocardiographic and angiographic images of the shunt vessels were identical. The ratio of the peak flow velocity measured at the aortic and the pulmonary ends of the shunt vessel was significantly larger in the segmentally stenosed shunt vessels than in the uniformly patent shunt vessels (p < 0.001). The ratio in the two shunt vessels only partially imaged by cross sectional echocardiography indicated that they were segmentally stenosed. CONCLUSION--The combination of cross sectional and Doppler echocardiography may be useful for determining either the patency or the morphology of an aortopulmonary shunt.