The objective of this paper is to assess the accuracy of audio signal Processing system in noninvasive automatic estimation of Pulmonary arterial pressure(PAP). Comparative studies among Doppler echocardiography, audio signal processing system (ASPS) and cardiac catheterization for predicting PAP have been done in 51 children with left-to-right shunting congenital heart disease. Estimated pulmonary artery systolic and mean pressure adopting modified pulmonary to aortic flow time interval ratios (F PA /F AO ) by ASPS correlated highly with those measured by cardiac catheterization (r = 0.95,0.96, p < 0.001), were correlated better than those measured by Doppler echocardiography (r = 0.86,0.86, p < 0.001). PAP can be estimated noninvasively adopting modified F PA /F AO by ASPS.