Pulsed Doppler echocardiography was utilized to elucidate the characteristics of pulmonary arterial (PA) blood flow in five patients without apparent pumping chambers in their right heart circulation after right heart bypass surgery for univentricular heart. Two of these patients underwent total cavopulmonary shunt operation, in which the total systemic venous return drained directly into the PA, bypassing the right atrium and ventricle. Three underwent the modified Fontan procedure with atrial partition, in which the right-sided atrium was reconstructed merely as a pathway from the vena cava to the PA, and atrial contraction was nearly entirely excluded. The flow pattern in the PA was biphasic and forward in all five patients. Pulmonary regurgitation was not observed in any of the patients. The first phase of PA flow had its peak during atrial systole; the second, during ventricular systole. Simultaneous observation of PA flow and pressures demonstrated an inverse relation between PA flow and pressure. Pulmonary venous (PV) blood flow pattern was also biphasic and similar to the PA blood flow pattern with time lags. In conclusion, in cases without pumping right heart chambers, PA flow reflects PV flow resulting from contraction and relaxation of the left atrium and ventricle.