Systemic haemodynamics in three infants with severe cardiac failure secondary to vein of Galen malformation (VGAM) were studied using two-dimensional and Doppler echocardiography. In all cases, ventricular outputs were over two times normal and superior vena caval flows up to 10 times normal reflecting high flow through the low-resistance fistula. Severe pulmonary hypertension, right heart dilatation and retrograde flow in the descending aorta were uniformly present. Systemic blood flow below the head and neck was reduced resulting in metabolic acidosis at presentation. Two infants had patent arterial ducts, in which flow was entirely right to left and on entering the aorta passed predominantly retrogradely towards the VGAM. These findings provide a basis for understanding the pathophysiology of cardiac failure in VGAM and support treatment with pulmonary and systemic vasodilating agents.