The pulmonary artery blood flow was determined in 40 dogs by pulsed Doppler echocardiography as a non-invasive means for estimating pulmonary artery pressure. Most of these dogs had become infected with heartworm disease which has been known to often cause pulmonary artery hypertension. From the flow velocity profile, four parameters, i.e., the Doppler tracing pattern, right ventricular ejection acceleration time (AT), and the ratios of AT to heart rate (AT/HR) and right ventricular ejection time (AT/ET), were obtained and their correlations with the pulmonary artery pressure determined invasively were investigated. Although the morphological pattern of flow velocity hardly allowed quantitative estimation of the pulmonary artery pressure, a relatively good negative correlation (P < 0.01) was obtained between the systolic pulmonary artery pressure and AT (r = 0.71), AT/HR (r = -0.67) or AT/ET (r = -0.84). The present results indicate that pulsed Doppler echocardiography is applicable to the estimation of pulmonary artery pressure and that AT/ET has the closest correlation with directly measured pulmonary artery pressure.