The purpose of this study was to evaluate a noninvasive method for estimation of pulmonary artery pressures in infants and children with interventricular communications. Systolic pulmonary artery pressures measured by cardiac catheterization were compared with those estimated by Doppler echocardiography. Pressure drops were measured by Doppler study (modified Bernoulli equation) and were referenced to systolic systemic arterial pressure measured by sphygmomanometry. All 25 patients in this study had either a ventricular septal defect or a single ventricle. The systolic pulmonary artery pressure measured by cardiac catheterization ranged from 15 to 100 mm Hg (mean +/- SD 44 +/- 26) and that measured by Doppler echocardiography ranged from 5 to 100 mm Hg (mean 43 +/- 26) (p = NS; r = 0.92; SEE = 9.9; slope = 0.92; y intercept = 4.7). Systolic pulmonary artery to aortic pressure ratio measured by cardiac catheterization ranged from 0.2 to 1.0 (mean 0.5 +/- 0.3) and that measured by Doppler echocardiography ranged from 0.1 to 1.0 (mean 0.5 +/- 0.3) (p = NS; r = 0.94; SEE = 0.09; slope = 0.90; y intercept = 0.04). This study demonstrates that Doppler echocardiography can closely approximate systolic pulmonary artery pressure in patients with interventricular communications.