AIM To evaluate the reliability of Doppler echocardiography in assessing pulmonary systolic pressure and analyze the problems compared with the right heart catheterization. METHODS Seventy three patients were clinically diagnosed as with primary pulmonary hypertension (PPH) underwent right heart catheterization and Doppler echocardiography to measure the maximal systolic pressure gradient between the right ventricle and right atrium (Δ p ). The data from Doppler echocardiography and catheterization wer...