Noninvasive estimation of the ratio of pulmonary to systemic flow in atrial septal defect by Duplex Doppler echocardiography. - Kitabatake,A.; Inoue,M.; Asao,M.; Ito,H.; Masuyama,T.; Tanouchi,J.; Morita,T.; Hori,M.; Yoshima,H.; Ohnishi,K. (Circulation, 1984)