Analysis of the systolic flow velocity curve (SFVC) in the right ventricular outflow tract is considered as an alternative to the tricuspid valve pressure gradient (TVPG) method for echo-Doppler assessment of pulmonary arterial pressure (P(pa)). The present study checked whether or not SFVC is affected by the cause of pulmonary hypertension. Doppler recordings of 86 patients (39 female, aged 55.5+/-15.2 yrs) with acute (AP-PE) or chronic (CP-PE) proximal pulmonary embolism, chronic obstructive pulmonary disase (COPD) or primary pulmonary hypertension (PPH) were retrospectively analysed by two observers unaware of the purpose of the study. Despite having the lowest TVPG (48+/-13 mmHg), patients with AP-PE had the shortest acceleration time (t(acc); 56+/-15 ms) and time to midsystolic deceleration (t(msd); 105+/-16 ms). t(acc) <60 ms in patients with TVPG <60 mmHg had 98% specificity and 48% sensitivity for AP-PE. In PPH, SFVC was less abnormal (t(acc) 64+/-14 ms, t(msd) 125+/-25 ms, both p<0.03) despite having a TVPG twice as high (92+/-12 mmHg, p< 0.001). In contrast to t(acc), TVPG showed strong correlation with direct P(pa) measurements whenever performed (r=-0.43, p=0.02, versus r=0.80, p<0.001; n=30). There was no correlation between t(acc) and TVPG in a pooled study group and SFVC seemed strongly affected by the presence of both AP-PE and CP-PE. While potentially useful for evaluation of the true right ventricular afterload during pulsatile flow conditions, the systolic flow velocity curve does not provide a reliable estimate of pulmonary arterial pressure.