Two babies with severe cardiac failure caused by a large arteriovenous malformation of the vein of Galen were evaluated with 2-dimensional ultrasound, pulsed and colour Doppler techniques. In both cases similar findings were recorded: dilated right cardiac chambers with high cardiac output in superior vena cava and ascending aorta; retrograde diastolic flow in descending aorta and continuous forward flow in arch arteries reflecting low resistance to flow in cerebral arteries; recirculation of microbubbles through the superior vena cava after passage unchanged through the cerebral malformation following contrast injection of saline into a peripheral vein or an arterial umbilical line. In addition, colour Doppler study of the brain clearly showed the malformation and the dilated straight sinus. Arteriovenous malformation of the vein of Galen can be noninvasively and easily detected by ultrasound studies of the heart and the brain.