Echocardiographic estimates of left atrial pressure (LAP) using the Q-C/A2-E ratio were obtained from 40 patients and compared with directly recorded mean LAP and/or pulmonary wedge pressure (PWP). The best correlation was obtained between LAP and the Q-C/A2-E (gamma = 0.95, P < 0.01); a good one between PWP and the Q-C/A2-E in normal and moderate pulmonary hypertension (gamma = 0.82, P < 0.01), but a poor one in severe pulmonary hypertension (gamma = 0.61, P > 0.05). Consequently, echocardiography provides a useful noninvasive method for the estimation of the LAP and PWP, particularly appropriate for children Intensive Care Unit.