Doppler ultrasound examination was performed in 69 patients with a variety of cardiopulmonary disorders who were undergoing bedside right heart catheterization. Patients were classified into two groups on the basis of hemodynamic findings. Group I consisted of 20 patients whose pulmonary artery systolic pressure was less than 35 mm Hg and Group II consisted of 49 patients whose pulmonary artery systolic pressure was 35 mm Hg or greater. Tricuspid regurgitation was detected by Doppler ultrasound in 2 of 20 Group I patients and 39 of 49 Group II patients (p less than 0.001). Twenty-six of 27 patients with pulmonary artery systolic pressure greater than 50 mm Hg had Doppler evidence of tricuspid regurgitation. In patients with tricuspid regurgitation, continuous wave Doppler ultrasound was used to measure the velocity of the regurgitant jet, and by applying the Bernoulli equation, the peak pressure gradient between the right ventricle and right atrium was calculated. There was a close correlation between the Doppler gradient and the pulmonary artery systolic pressure measured by cardiac catheterization (r = 0.97, standard error of the estimate = 4.9 mm Hg). Estimating the right atrial pressure clinically and adding it to the Doppler-determined right ventricular to right atrial pressure gradient was not necessary to achieve accurate results. These findings indicate that tricuspid regurgitation can be identified by Doppler ultrasound in a large proportion of patients with pulmonary hypertension, especially when the pulmonary artery pressure exceeds 50 mm Hg. Calculation of the right ventricular to right atrial pressure gradient in these patients provides an accurate noninvasive estimate of pulmonary artery systolic pressure.