Doppler echocardiography is a commonly used non-invasive method for assessing pulmonary hypertension (PH). However, this study found that Doppler estimates of pulmonary artery systolic pressure (PASP) and cardiac output (CO) can be inaccurate. The study involved 65 patients with PH who underwent Doppler echocardiography within one hour of right-heart catheterization. Using Bland-Altman analysis, the bias for Doppler estimates of PASP was -0.6 mm Hg, with 95% limits of agreement ranging from +38.8 to -40.0 mm Hg. Doppler estimates were inaccurate (greater than ±10 mm Hg of invasive measurements) in 48% of cases. Overestimation and underestimation of PASP occurred with similar frequency. The magnitude of underestimation was greater than overestimation, and underestimates often led to misclassification of PH severity. For CO, the bias was -0.1 L/min with 95% limits of agreement ranging from +2.2 to -2.4 L/min. The study concluded that Doppler echocardiography may frequently be inaccurate in estimating PASP and CO in patients with PH. The accuracy of Doppler estimates was influenced by factors such as right atrial pressure estimation and poor Doppler imaging of the tricuspid regurgitant jet. While Doppler echocardiography is a useful screening tool, it may not always provide accurate hemodynamic assessments, and right-heart catheterization remains the gold standard for definitive diagnosis. The study highlights the importance of using Doppler echocardiography in conjunction with other diagnostic methods and emphasizes the need for careful interpretation of Doppler results, particularly in cases where the quality of the Doppler signal is poor. The study also found that Doppler estimates of CO were less reliable, with wide 95% limits of agreement. Overall, the study underscores the limitations of Doppler echocardiography in the hemodynamic assessment of PH and the importance of using right-heart catheterization for accurate diagnosis.Doppler echocardiography is a commonly used non-invasive method for assessing pulmonary hypertension (PH). However, this study found that Doppler estimates of pulmonary artery systolic pressure (PASP) and cardiac output (CO) can be inaccurate. The study involved 65 patients with PH who underwent Doppler echocardiography within one hour of right-heart catheterization. Using Bland-Altman analysis, the bias for Doppler estimates of PASP was -0.6 mm Hg, with 95% limits of agreement ranging from +38.8 to -40.0 mm Hg. Doppler estimates were inaccurate (greater than ±10 mm Hg of invasive measurements) in 48% of cases. Overestimation and underestimation of PASP occurred with similar frequency. The magnitude of underestimation was greater than overestimation, and underestimates often led to misclassification of PH severity. For CO, the bias was -0.1 L/min with 95% limits of agreement ranging from +2.2 to -2.4 L/min. The study concluded that Doppler echocardiography may frequently be inaccurate in estimating PASP and CO in patients with PH. The accuracy of Doppler estimates was influenced by factors such as right atrial pressure estimation and poor Doppler imaging of the tricuspid regurgitant jet. While Doppler echocardiography is a useful screening tool, it may not always provide accurate hemodynamic assessments, and right-heart catheterization remains the gold standard for definitive diagnosis. The study highlights the importance of using Doppler echocardiography in conjunction with other diagnostic methods and emphasizes the need for careful interpretation of Doppler results, particularly in cases where the quality of the Doppler signal is poor. The study also found that Doppler estimates of CO were less reliable, with wide 95% limits of agreement. Overall, the study underscores the limitations of Doppler echocardiography in the hemodynamic assessment of PH and the importance of using right-heart catheterization for accurate diagnosis.